Morning Joe slams ‘stupid‘ Trump’s attacks on Warren’s heritage: ‘What the hell’s wrong with them?’

Elizabeth Warren has demonstrated a unique ability to get under Donald Trump's skin -- which she mocks as "thin" and easily permeated -- and the Republican candidate has responded the only way he knows how: with obnoxious insults.

Trump repeatedly responds to the Massachusetts senator's criticism by calling her Pocahontas, a slur against her Native American heritage -- and a tactic MSNBC's "Morning Joe" argued was both lame and insulting.

Scott Brown, who lost his re-election bid to Warren in 2012, has come to Trump's aid by calling on the senator to prove her Native American ancestry with a DNA test.

"This is when you know you're losing a debate," said host Joe Scarborough. "When your opponent is talking about working class Americans, and fighting hard to bring working class Americans back into the mainstream of American economic life, and you are talking about whether someone is 1/32 Native American and suggesting DNA testing."

Scarborough said the attacks against Warren's racial background were a bizarre and ineffective distraction.

"What the hell's wrong with them -- are they stupid?" he wondered. "Are they stupid?"

Co-host Mika Brzezinski said Trump had promised to act more presidential now that his campaign has pivoted to the general election -- but that hasn't happened yet.

"They say they're going to turn the page and pivot toward the general election and have a more elegant -- but, you know, you can't if your candidate is releasing ridiculous, cartoon-like, kindergarten-like statements," Brzezinski said.

"If you're going to turn the page, you turn the page -- and they're trying to turn the page, especially on the Muslim ban," Scarborough said. "But you can't keep turning back. Turn the page, and then keep moving forward. That's the discipline -- they've got to be disciplined up and down the line. This 'Pocahontas' nonsense, this 'goofy' nonsense, they've got to stop -- it doesn't work. It makes them look small in the general election."

Trump calls Warren 'Pocahontas'... @JoeNBC: If you're going to turn the page, you can't keep turning back https://t.co/TIzb0LtvG5

— Morning Joe (@Morning_Joe) June 28, 2016