(CNN) When Adam Schiff was poised to take over the House Intelligence Committee late last year, he spoke about his desire to restore comity to the panel after two years of infighting over the Russian investigation.

Three months into the new Democratic Congress, the committee's partisan warfare is more intense than ever.

Schiff, the 10-term California Democrat, became the face of Democrats' probing of President Donald Trump during the first two years of his presidency, elevating his national profile and making Schiff a staple on TV and in op-ed pages whenever new developments were revealed about contacts between Trump associates and Russians.

But now that special counsel Robert Mueller's investigation did not establish a criminal conspiracy between Trump's team and the Russian government, according to a summary released Sunday by Attorney General Bill Barr, the Republicans who long bristled at Schiff have dialed their attacks up to 11.

Trump attacked Schiff at his rally Thursday and tweeted that he should resign from Congress. House Republican leaders on Monday began calling for Schiff to step down as chairman of the Intelligence Committee. One Republican on the panel compared Schiff's collusion comments to former Sen. Joe McCarthy's 1950s communism hunt.

And on Thursday, the nine Republicans on the House Intelligence Committee announced at the start of a public hearing they had signed onto a letter calling for Schiff's resignation from his position.

"Your actions both past and present are incompatible with your duty as chairman of this committee," said Texas Rep. Mike Conaway, who ran the Republican-led Russia investigation with Schiff in the last Congress, reading the letter aloud at the hearing. "We have no faith in your ability to discharge your duties in a manner consistent with your constitutional responsibility and urge your immediate resignation as chairman of this committee."

While he has faced GOP criticism before, Thursday's hearing represented an escalation of the scrutiny Schiff faces as a leader of Congress' continued investigation into Trump and Russia in a post-Mueller-probe Washington.

Schiff fights back

Schiff has shown no sign of backing down.

Anticipating the ambush Thursday, Schiff delivered an impassioned rebuttal to the Republican letter by ticking through a litany of alleged offenses, including the June 2016 Trump Tower meeting where a Russian lawyer offered "dirt," Trump calling on Russia to hack Hillary Clinton's emails, Roger Stone's alleged communications with WikiLeaks and former national security adviser Michael Flynn lying about talking sanctions with the Russian ambassador to the US.

"You might say that's all OK. You might say that's just what you need to do to win," Schiff said. "But I don't think it's OK. I think it's immoral, I think it's unethical, I think it's unpatriotic, and yes, I think it's corrupt, and evidence of collusion."

This is not the first time that lawmakers have been at each other's throats on the House Intelligence Committee. In fact, two years ago this month, it was Democrats calling on then-Chairman Devin Nunes to recuse himself from the Russia investigation after the California Republican made a clandestine trip to the White House and said he obtained evidence that the Obama administration gathered surveillance on the Trump campaign.

Nunes temporarily stepped aside from the Russia investigation, though he remained chairman and is now the panel's top Republican. But the episode created a culture of distrust and suspicion on the committee that festered through the course of the year-long Russia investigation and the 2018 release of the classified "Nunes memo" alleging FBI foreign surveillance law abuses.

Lawmakers on the committee say they are mostly able to set aside their differences on matters unrelated to the Russia investigation. But even that will be put to the test amid the latest fight over Mueller, Russia and collusion.

Perhaps the sharpest sign of the tension on the committee came Thursday when Rep. Mike Turner, an Ohio Republican, accused Schiff of "McCarthyism."

"With McCarthyism, we had Russia chasing after Russian communists," Turner said at the hearing. "And now we have Schiff chasing after Russian collusion and those who would collude."

Schiff has shown no indication he is considering stepping aside, and House Speaker Nancy Pelosi has vehemently defended the chairman Thursday, accusing Republicans of being "afraid of the truth."

What happens now?

Schiff plans to move forward with his sweeping investigation into the President that he unveiled last month. The investigation includes a probe into Trump's finances, something he's suggested goes beyond the scope of the Mueller probe.

But Republicans have seized on Barr's summary of the Mueller report to press Schiff to end his investigation and accuse him of lying when he claimed he had evidence of collusion.

"Go look at all the tape from every national TV show you can imagine, of some of the most outlandish claims that were made and now the Mueller report comes out and it's clear those claims are baseless. There was no collusion," said House Minority Whip Steve Scalise.

Schiff has responded to the criticism by arguing there's a distinction between Mueller's criminal investigation and the counterintelligence investigation into Trump's team. Even if Mueller did not establish a criminal conspiracy, Schiff said, there has been evidence of collusion.

"What the Barr letter says is Mueller could not establish a criminal conspiracy. ... It doesn't meant there's not evidence. There is," Schiff said. "I think these interactions with the Russians that I enumerated earlier are evidence of ... collusion. But that whether that amounts to proof beyond a reasonable doubt of a crime, the crime of conspiracy, I've always said is a different question."

Thursday's hearing was held with policy experts, including former US Ambassador to Russia Michael McFaul, to discuss Russian money laundering. But the hearing became a de facto committee debate about the Russia investigation, with several Republicans engaging with Schiff at length rather than posing questions to the witnesses.

Schiff debated, for instance, Rep. Will Hurd, a Texas Republican and former CIA officer, over the Republican committee findings raising questions about the intelligence tradecraft in the intelligence community assessment that Russia helped Trump win in 2016.

Schiff had a more cordial discussion with Rep. Chris Stewart, a Utah Republican, about evidence of collusion, where Schiff argued that his public statements had made a clear distinction between uncovering evidence of collusion and Mueller's investigation into a criminal conspiracy.

But Stewart didn't buy it.

"We can find evidence of all sorts of things," Stewart said, "but if it doesn't reach a legal threshold, then it's meaningless."