kidney problems, or high potassium in your blood. ♪ tomorrow, tomorrow... ♪ when can we do this again, grandpa? well, how about tomorrow? ask your doctor about entresto and help make tomorrow possible. well, the breaking news tonight, a boastful presidential tweet about nuclear weapons. to reiterate, the president just tweeted this. "north korean leader kim jong-un stated the nuclear button is on the table at all times. will someone if his depleted and food-starved regime please inform him i, too, have a nuclear button but it is a much bigger and more powerful one than his and my button works." back with gordon chang of the center for strategic and international studies. also joining us is cnn senior political analyst david gergen. david, as someone who's worked for presidents, both republican and democrat, what do you make of this tweet? >> well, first of all, anderson, it's good to see you.