What sparked the fire and the Quick Response overnight. The sisters are doing it for themselves. Venus and Serena Williams about to go headtohead in the Australian Open final. Shes my toughest opponent. Everyone has their moment in the sun. Both of them on the verge of history, serena playing for the most singles titles ever for a woman, only venus standing in her way. Game on in this epic sibling showdown. Sisters are doing it for themselves sisters are doing it for themselves. Sister act, great to have david here. Great to be here. Nothing elsgoing on. How about this epic battle coming up with the wilams sisters . Cant wait for that. Back in action and i love what venus said about serena. Tough talk about her opponent but then she said shes super awesome soant wait for that. A big week for the president too here and another busy day overnight. Headlines coming in right now. President trump took his first flight on air force one and gave the press a rare look inside the oval office in the sky. Beautiful, great plane. Really beautiful. This is a very special plane for a lot of reasons. Outside of just being a plane. As we said its been a busy first full week for the president and this morning a kremlin spokesman confirms that President Trump and president putin will speak tomorrow. And there is a question about a phone call the president made to the National Park service after the inauguration. But lets start with cecilia vega on the escalating war of words with mexico. Good morning, cecilia. Reporter yeah, robin, good morning to you. This is, of course, all about that wall and who pays for it, the u. S. And mexico, one of our most important allies and trading partners at a standoff this morning but as one foreign leader cancels a visit to the white house today, another one is headed here. Despite a potential diplomat disaster with americas neighb to the south, President Trump overnight offering strong words about his plans to build that wall. Im talking about a real wall. Im talking about a wall thats got to be like serious and even that, of course, youll have people violated but well have people waiting for them when they do. Reporter in an interview with fox news the president not backing down. Look, the wall is necessary. Thats not just politics. And yet it is good for the heart of the nation in a certain way because people want protection and a wall protects. Reporter but this morning the white house seems to be uncertain over ideas about how to pay for that wall. Press Secretary Sean Spicer first telling reporters aboard air force one the president is considering a hefty 20 tax on goods imported from mexico, part of a proposed tax overhaul. We can do 10 billion a year through that mechanism alone. Reporter republicans and democrats outraged fearing the cost pay be passed on to American Consumers and Lindsey Graham tweeting any policy proposal which drives up costs of corona, tequila, or margaritas is a big time bad idea. Mucho sad. The white house forced to clarify saying it was just one way the wall could be paid for. Ive said many times that the American People will not pay for the wall. And ive made that clear to the government of mexico. Reporter mexicos president , not happy. He abruptly backed out of next weeks visit to the u. S. Trump telling republican lawmakers in philadelphia the cancellation was mutual. Unless mexico is going to treat the United States fairly with respect, such a meeting would be fruitless. Reporter but mexicos president took to twitter saying he canceled the meeting. And uk Prime Minister theresa may headed here today. This is, of course, President Trumps first meeting with a foreign leader since he took office and some of his comments on torture and America First are putting may in a very difficult position, robin. All eyes on that press conference here at the white house in just a few hours. And we will, of course, carry it here on abc live and theres also been a lot of talk about the socalled sanctuary cities and appears the mayor in miami will follow through with what the white house wants. Reporter this is a response to the president s plan to gut funding for sanctuary cities ordering county jails to comply with immigration requests and that would gut that citys sanctuary city program. The presiden calling this, all right, cecilia, thank you. Well, robin, its been exactly one week since President Trump took office and lets bring in jonathan karl. We learned about a phone call between President Trump and the head of the National Parks service. Talking about the inaugural crowd. Reporters were summoned into the Briefing Room and told this was the largest audience to witness an inauguration, period. I am curious about the first full day here at the white house. Choosing to send the press secretary out into the Briefing Room summoning reporters to talk about the inaugural crowd size, does that send a message to the American People that thats more important than some of the very pressing issues . Part of my whole victory was that the men and women of this country who have been forgotten will never be forgotten again. Part of that is when they try and demean me unfairly because we had a massive crowd of people. We had a crowd i looked over that sea of people and i said to myself, wow. And, jon, now weve learned of a phone call between the president and that acting director at the National Park service. Reporter on saturday morning, david, i mean, just hours after he is sworn in as president of the United States hes on the phone with the park service about those photographs and about the crowd size looking for evidence that the crowd was bigger. I mean its amazing. He probably hadnt even unpacked his bags yet, remember, he was up late the night before at the balls, of course, his inauguration speech and this is what hes talking about, but, you know, its not surprising at all. Donald trump has been fascinated by his crowds from the start. He has drawn some of the biggest crowds we have ever seen as a president ial candidate. As a matter of fact if theres one thing nobody should ever doubt its trumps ability to draw a crowd. But its clearly something he draws energy from and something of an obsession here. Let me ask you about steve bannon, President Trumps chief strategist adviser in the white house. He talked yesterday pretty angry. Reporter yes, no doubt talking to the new york times, talking about the press as if as an opposition party, not the democrats, its the press that is our opposition. Suggesting that the press should keep their mouth shut. Fascinating because the Trump White House has been very open so far in the first week giving a lot of access actually more access than i saw in the Obama Administration to the White House Press corps. Thanks, j lets bring in terry moran who joins us from london and we know about the Prime Minister the british Prime Minister going to talk to donald trump meeting with him, the first time a foreign leader will be there p think . Reporter well, the whole world will be watching that meeting, robin. It is President Trumps diplomatic debut and World Leaders looking for clues about how to deal with a guy they dont know or understand and we expect Prime Minister theresa may to remind President Trump of that close history that the u. S. And Great Britain share. Shes also looking for a trade deal after british voters chose to leave the european union, but shes also under tremendous pressure to stand up to President Trump on the issue of torture and some of the rest of his agenda and she will be speaking for many people throughout americas traditional allies when she does that. Terry, the kremlin has confirmed that president putin will be talking to President Trump on the phone on saturday. What do you make of that . Reporter well, this is the first phone call and it is a big one. The kremlin is confirming that itll happen tomorrow. They say president putin wants to congratulate President Trump on his inauguration. Theyll discuss a whole range of issues, president putin wants the end to the sanctions slapped on russia after russia seize crimea and President Trump says he wants help in fighting isis and islamic extremism and reducing nuclear weapons. They have a lot to talk about and this will be apparently the first time they spoke. Fascinating to watch them, the two of them side by side. That march for life, a live look at the stage set in washington, d. C. Where speakers will gather to protest abortion, Vice President mike pence is expected to address the rally today and abcs mary bruce is live at the National Mall with more for us. Hey, mary. Reporter good morning. In just a few hours this whole area will be flooded with demonstrators and this year they feel they really have something to celebrate, now that donald trump is in office their wish list could become a reality. Theyre calling on him to appoint an antiabortion Supreme Court justice and want to ban federal funding for many abortions and in a sign of just how powerful this movement is that headliner here this morning, Vice President mike pence. David. Windy d. C. Behind you, we can see, mary, but a lot of focus on this march because as you know we asked the president about the other march, the womens march the day after he was sworn in and we wondered if he he has a sense of responsibility for trying to unite the country. Could you hear them . No, i couldnt hear them but the crowds were large but youre going to have a large crowd on friday too which is mostly prolife people. Youre going to have a lot of people coming friday and i will say this and i didnt realize this but i was told you will have a very large crowd of people. I dont know, as large or larger. Some people say it will be larger prolife people and they say the press doesnt cover them. I dont want to compare crowd sizes again. No, you shouldnt but let me tell you they do say that the press doesnt cover them. We saw the marches around the country and you are their president now. Do you sense the responsibility to reach out now and to unite them and for those women, men, children who marched who are watching this what would you say to them. Well, i do but i have to also say we just had an election a few weeks ago. And they voted in many cases and in some cases they didnt vote, i imagine. And we did have an election. With that being said, absolutely i have responsibity to everybody including people that didnt vote for donald trump. Totally. A responsibility to everybody but you heard the president there say, mary, this crowd could be as large or even larger talking about the crowd size. Yeah, the president clearly hoping for a big turnout here today. He has high hopes for this march. But, david, these demonstrators have high hopes for him and want him to follow through and that is a message they will be making loud and clear this morning. Mary, thanks so much and to the whole team. Well carry that News Conference live today, President Trump and the Prime Minister of britain. The press conference right here on abc. Well see you for that. Michael. All right and now to that health alert about mumps outbreaks across the country, at least 90 cases in one Washington City and the cdc says almost half the cases this year are in the state of arkansas alone so dr. Besser is here to talk about it. Dr. Besser, theres a vaccine against mumps so, you know, why are these outbreaks happening . Its a great question. If you get two doses of the vaccine it protects about 88 of people. Its not 100 effective. One dose only 78 so over time, theres a group of people that builds up who are at risk of this vaccine and you tend to see these outbreaks in crowded places, schools, places where people are living closely and can share viruses. You know, the number of cases that have gone fivefold between 2015 and 016 but why is that as well. Yeah, in 2016 there were more than 5,000 case, 2015, about a thousand cases. You look at some of these other years, the chart, in the hundreds so people are wondering. There is a number of theories, one is that the virus may be changing. So that maybe the vaccine isnt as good as a match. The other, as people get older their immunity goes down and a third, maybe doctors arent storing the vaccine properly. It has to be kept cold before you give it. If they dont it could be less effective but they havent sorted that out. Remind us why should we worry about the mumps. For most people its an annoyance, its fever, its body aches, its swelling of your jaw. If you get it when youre older youre at risk of getting meningitis or encephalitis, the swelling of the brain, some deafness, could cause inflammation of the testes or ovaries. You want to reduce your risk as much as you can. Thanks for those symptoms. That midair emergency overnight, a plane from washington, d. C. Forced to make an Emergency Landing in nashville after a fire broke out in one of the engines. Right to david kerley at Reagan National airport for us. Good morning, david. Reporter good morning, robin. Some tense moments on that flight into nashville. The crew declaring an Emergency Landing as theyre approaching because in flight, they got a warning of a fire in one of their engines. We are declaring an emergency. We have a right engine fire. Be advised we do have a fire warning and the fire is still out. We were not able to extinguish it. The flight attendantsn ot o the horn and sai hwere going to emergency land. Head down, grab your ankles. Head down kept repeating it. Reporter as soon as the jet landed the doors were open and stairs brought up and the passengers were able to evacuate and firefighters went to that engine. They sprayed on water and foam. They say there were no flames but they called it a hot spot in the engine. Nobody was injured and Mesa Airlines which operated this United Express flight says it took that jet out of service. Theyre going to check the engine, of course, robin. Of course and as you said thankfully no one was injured. Thanks so much. There were frightening moments for people staying at a Popular Hotel in tampa, florida. Flaming pouring from the roof of the Marriott Hotel downtown forcing hundreds to evacuate and investigators say debris from construction work likely sparked that fire. No injuries reported. Crews were able to stop the fire from spreading to the inside of the building. And now to the sister showdown. Lets do it. Sisters are doing it for themselves. Venus and Serena Williams are hours away from facing off for the Australian Open title match and paula faris is here with a closer look at whats on the line. Good morning, paula. Good morning. I heard you said lets do this. Thats right. This was the first time the williams sisters would go headtohead. Also at the aussie open back in 1998. Look how young they were. Venus 17, serena just 16. Big sister won that day. Telling serena afterwards, quote, im sorry i had to take you out. Venus williams aced her way into tennis history. 11 aces now. Reporter defeating Coco Vandeweghe in a grueling threeset battle. To become the oldest Australian Open finalist of all time. No need to contain the joy, venus. She cant believe it. The only one who can steal her thunder down under is her little sister, serena, who at age 35 cruised her way to the finals with a series of straightset victories. Shes my toughest opponent. No one has ever beaten me as much as venus has. Shes basically my world and my life. Reporter venus has been the comeback kid after being diagnosed with a careerthreatening auto immune illness six years ago now ranked 17th in the world. Everybody has their moment in the sun. Maybe mine has gone on a while but id like to keep that going. I got nothing i got nothing else to do so reporter the sisters first went headtohead at the australian 19 years ago, venus won that match but since then serena has a 1611 alltime advantage. The last time they took each other on in a grand slam final it was wimbledon in 2009. It is hers. Reporter if serena wins it will be her 23rd grand slam singles title, the most of any woman in the open era but can she pull out another victory over the sister she loves so much . I just feel like no matter what happens weve won because a williams is going to win this tournament. Reporter she is the oldest to compete at the aussie open final and has no plans of riding off into the sun set. At least not yet. She has her eyes set on playing in the 2020 olympics in tokyo and would be almost 40 years old. Why not. Why not. Yeah, exactly. So old. We know what venus is going to do. What is serenas next move . Serena has a little bling on her finger. She announced her engagement to reddit cofounder A