Rep. Adam Schiff is facing calls to step down as chairman of the House Intelligence Committee over his repeated claims to have evidence of Trump-Russia collusion.

In a letter, obtained by Fox News and signed by every Republican on the House Intelligence Committee, lawmakers slammed Schiff (D-Calif.) for his claims in the media that there was “more than circumstantial evidence” of collusion between the Trump campaign and Russia. They repeated their demand in person during a feisty hearing Thursday morning.

President Trump himself went even further than congressional Republicans Thursday morning, tweeting Schiff "should be forced to resign from Congress."

On "America's Newsroom" Thursday, Fox News contributor Newt Gingrich said Schiff is "totally, profoundly dishonest."

He said that Trump and his advisers should consider sending a letter to House Speaker Nancy Pelosi informing her that the executive branch will not with the Intelligence Committee while Schiff is a member.

"We don't have to sit around and pretend that this is acceptable," Gingrich said. "This is a direct assault on the American system. We now know it was a direct assault because after two years, 500 subpoenas, millions of dollars, you have a Mueller report that says there was no collusion."

Schiff has doubled down this week on his belief that Trump and his administration colluded with Russia, despite Attorney General William Barr announcing that Mueller did not find that collusion occurred.

"Undoubtedly there is collusion," he told the Washington Post.

At the hearing Thursday morning, Schiff spoke in his opening remarks about how the Trump campaign acted inappropriately in 2016 by trying to obtain "dirt" on Hillary Clinton from the Russians. He focused on the Trump Tower meeting between a Russian lawyer, Trump's son and others.

"You might think it's OK that their only disappointment after that meeting was that the dirt they received on Hillary Clinton wasn't better. You might think it's OK ... I don't," he said, laying out other contacts between the campaign and Russians. 

Watch more from Gingrich above.

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