grandmother's basement in arlington. >> the saturday night massacre was a disaster for richard nixon, and one of the worst decisions he made as president. he didn't set it up. he didn't brace people. no one really understood why he was doing it. he was doing it because cox was challenging his presidential authority. >> i think everybody had questions. where is this going to go? is the rule of law under serious attack? are we going to get justice here? is nixon going to get away with this? >> and the thing is what do you do with a president who insists on firing somebody? >> special counsel robert mueller has been investigating whether trump's campaign included with russia. trump has criticized mueller's investigation as a witch hunt. >> it's a dangerous, dangerous thing when you're able as the president of the united states to get rid of those people that are investigating you. simply because they're not on your agenda. >> president trump could instruct his attorney general to fire robert mueller. but because of his role in the campaign, sessions recused