carey. former republican presidential nominee, mitt romney has jumped into the republican civil war, attacking g.o.p. front runner, donald trump's character, calling him a fraud and a phony. >> there's plenty of evidence that mrump is a conman, a fake. mr. trump has changed his positions not just over the years, but over the course of the campaign, and on the ku klux klan daily for three days in a row. we will only really know if he is a real deal or a phony if he releases his tax returns. >> donald trump tweeted, of course, that he would be in the air the next two hours, flying to a campaign event in maine. however, earlier he tweeted this: and then speaking on msnbc this morning, trump said that romney, that's a quote, for his endorsement in 2012. >> he failed at his campaign. it was a horribly-run campaign. he was a disaster the last month, month and a half. he wasn't on television. it was almost like he was lost, and he ran one of the worst campaigns as you know in presidential history. in that was an election that should have been won by the republicans. he was a catastrophe. >> joining me now is david shuster. >> remarkable, right? >> shocking that donald trump would speak of mitt romney that way. but o