'Morning Joe' can't believe Trump is still taunting GOP rivals: 'The stupidity is breathtaking'
Mika Brzezinski and Jo Scarborough (MSNBC)

Donald Trump lashed out at his former Republican presidential rivals who have not yet endorsed his campaign -- and MSNBC's "Morning Joe" added his latest vindictive attack to the list of disqualifying character traits.

"The stupidity is breathtaking," said host Joe Scarborough. "Here you have a guy that delivers a speech that actually can convert Democrats in Ohio and Pennsylvania and across the Rust Belt, and the next day -- because he's talking about people, he's talking about other people's jobs, he's talking about bringing jobs to America, he's not obsessed with the minutiae of politics. And then he goes off on GOP candidates -- they're not going to endorse him now. He keeps knocking them around like that, that's the last way to get people."

"Who cares? Who cares if Jeb Bush endorses him?" Scarborough continued. "Who cares if John Kasich endorses him? He's obsessed -- it's like when he was ahead in 49 states in polls but he was just losing in Iowa, he went to Iowa and he called people stupid. I wonder why he lost in Iowa. He said, 'What, are you stupid?' The guy, is he capable of being disciplined in moving on or not?"

Co-host Mika Brzezinski said Trump's erratic behavior could cause voters to fear him.

"People do vote their fears, they do, but they can't fear you," she said. "They can't fear that you're unhinged. They can't fear that you're inconsistent. They can't fear that you say one thing and you mean another. They can't fear that you'll just blurt out a lie, a blatant lie."

Scarborough broke in and imagined how Trump might conduct diplomacy if he's unable to let any petty insult to his fragile ego go unquestioned.

"They can't fear that in the middle of a conference over, let's say in Geneva, where you're negotiating something that's extraordinarily important to the United States, that you read an article and then you go off on (German Chancellor Angela) Merkel or you go off on somebody else the next day at a press conference," Scarborough said. "Does he have any discipline at all? Can he do the same thing two days in a row? Right now, the answer seems to be a resounding no."