On television, in Congress and before a crowd of thousands, President Donald Trump and Republicans are mounting a ferocious revenge campaign against one Democrat – representative Adam Schiff.

Moments after taking the stage at a Michigan campaign rally on Thursday night, Mr Trump mocked the California lawmaker as "little pencil-neck Adam Schiff." House minority leader Kevin McCarthy, R-Calif, compared Mr Schiff to communist scaremonger Joseph McCarthy. And House whip Steve Scalise, R-La, used a colloquy on the House floor to press majority leader Steny Hoyer, D-Md, to remove Mr Schiff as chairman of the House Intelligence Committee.

"There has to be accountability, because it's all lies," Mr Trump said to a crowd booing the mention of Mr Schiff's name. "And they know it's lies – they know it."

Together, the attacks levelled in the week since special counsel Robert Mueller III delivered his findings represent an unusually coordinated assault against the leading Democratic voice questioning whether Mr Trump and his associates had conspired with Russia to throw the 2016 election in his favour.

Mr Mueller had been Mr Trump's villain for nearly two years, with the president lashing out at the "conflicted prosecutor" and his "angry Dems" investigators engaged in a "phony witch hunt."

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Now, with attorney general William Barr's four-page summary of Mr Mueller's report indicating no conclusion of a criminal conspiracy, Mr Trump and Republicans have a new target for their vitriol.

The Trump campaign circulated a memo to TV producers on Monday questioning Mr Schiff's credibility, citing a litany of pronouncements that it claimed had been rebutted by Mr Mueller. Mr Trump on Thursday called for Mr Schiff to resign his House seat, accusing him of "knowingly and unlawfully lying and leaking," and the nine GOP members of the Intelligence panel signed a letter demanding he step down as chairman, questioning whether he was abusing his position and damaging the panel's integrity.

Mr Schiff has stood resolute amid the attacks, maintaining that there is public evidence of collusion – such as Mr Trump's public July 2016 plea to Russia to hack Democratic opponent Hillary Clinton's emails – even if Mr Mueller determined that evidence does not amount to a crime. When Republicans confronted Mr Schiff at an Intelligence Committee hearing on Thursday, he struck back.

"You might think that's OK – I don't," Mr Schiff said repeatedly as he recounted a litany of interactions between Trump associates and Russia. "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."

He has won uniform backing from House Democratic leaders, including speaker Nancy Pelosi, D-Calif, who called Republicans "scaredy-cats" for attacking Mr Schiff before the Mueller report is publicly released.

"What is the president afraid of? Is he afraid of the truth, that he would go after a member ... a respected chairman of a committee in the Congress?" she asked. "They just don't know what to do, so they have to make an attack."

The GOP's outsize attention on Mr Schiff reflects his two years of omnipresence on Sunday talk shows and weekday cable news programmes. The congressman who represents Hollywood has long been ribbed by Republicans – and privately, even by some Democrats – for his frequent appearances.

When Democrats were the minority party in the House, that tactic was intentional. Television was a "tool," Mr Schiff said last year, for "exposing what the majority's doing and often exposing what the majority's not doing."

Since taking over as chairman, he has scaled back his appearances, but he has not pulled any punches when it comes to voicing his belief that Trump subordinates' contacts with Russians, their clandestine finances, and the lies they told to lawmakers and federal law enforcement are evidence of likely wrongdoing, even if they do not rise to the level of a crime.

That caught Mr Trump's attention, making him a target of presidential derision with jeering nicknames like "liddle," "sleazy," and "Adam Schitt."In recent days, the president tried out the "pencil neck" insult at a White House meeting with House Republicans before using it at Thursday's rally, according to a White House official who spoke on the condition of anonymity to discuss private conversations.

"He's got the smallest, thinnest neck I've ever seen," Mr Trump said. "He is not a long-ball hitter."

The official Trump campaign on Friday rolled out a T-shirt with an image of Mr Schiff with a pencil for a neck and a red ball on his nose.

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For Republicans, the attacks on Mr Schiff are at least partial payback for months of Democratic attacks on the previous committee chairman, representative Devin Nunes, R-Calif, who oversaw a circumscribed probe of Russian ties to the Trump campaign and instead focused on Obama administration decisions that prompted the Justice Department probe.

"Important context is what happened to Devin Nunes," representative Matt Gaetz, R-Fla, said this week, pointing to Democratic pressure in 2017 after lawmakers found out that Mr Nunes made a late-night visit to the Trump White House to view classified materials pertaining to the Russia investigation.

When Mr Nunes publicly alleged that Mr Trump's affiliates may have been picked up in a federal wiretap, that prompted allegations that Mr Nunes had disclosed secret surveillance reports, spurring an Ethics Committee investigation that ultimately cleared him. But as the cloud grew, Mr Nunes said in April 2017 that he would recuse himself from the committee's Trump-Russia probe.

Later, Democrats accused Mr Nunes of destroying the credibility of the Intelligence panel and trying to use his subpoena power to undermine federal law enforcement as he sought to publicise the origins of the Trump-Russia probe.

Mr Schiff said this week it was imperative that lawmakers be able to determine whether Mr Mueller weighed all the evidence they are looking into, especially regarding money laundering and Mr Trump's plans to build a tower in Moscow during his presidential campaign.

But for the GOP, the matter is settled – and what goes around comes around.

"Here you have Mr Schiff, who essentially spent 22 months lying to the country," Mr Gaetz said. "I don't know how he's going to have credibility with the intelligence community."

Mr Nunes himself has been largely quiet about Mr Schiff, but his fellow Republicans have not been shy about raising the Democratic attacks on Mr Nunes.

"Didn't the Mueller report justify exactly what chairman Nunes has said?" Mr McCarthy asked on Thursday amid his attacks on Mr Schiff. "I think chairman Nunes comes out on top. The concerns that he had with what was being said, what was being done was just proven correct."

He added, referring to Mr Schiff and Mr Nunes respectively, "One member lied to the American public; one member told the truth and was attacked for it."

Mr Schiff knows as well as anyone the political perils of assuming a role as a presidential inquisitor: He won his seat in 2000 by ousting representative James Rogan, R-Calif, who was among the House managers of President Bill Clinton's 1999 impeachment trial. Mr Schiff capitalised on Democratic outrage to raise millions of dollars from donors across the country eager to exact revenge.

Senate Judiciary Committee chairman Lindsey Graham, R-SC, speaking in a Fox News interview this week, compared Mr Schiff to Jim Garrison, the New Orleans prosecutor who spent decades pursuing an unproven conspiracy to assassinate President John F Kennedy.

"Adam Schiff has got to make a decision about his political future," he said. "Does he want to be the guy that won't let it go when the authority of the investigation, Mr. Mueller, has concluded there was no collusion?"

But there is no indication Mr Schiff's pursuit of Mr Trump has caused him any political trouble in a district that preferred Ms Clinton by 50 percentage points in 2016 and re-elected him to a 10th term last year with 78 per cent of the vote.

Mr Schiff, in fact, has emerged as one of the Democratic Party's most talented fundraisers, with $4.7m (£3.6m) in his campaign account – more than any other sitting House member. This week, he was named a national finance chair for the Democratic Congressional Campaign Committee, aimed at holding the party's new majority.

House Democrats are not in full agreement about how forcefully they want to continue to pursue the Russia matter now Mr Mueller has completed his report. But they are unanimous in their defence of Mr Schiff and their insistence that Mr Trump is not in the clear until they can see the full extent of the special counsel's findings.

As Mr Scalise pressed Democrats to remove Mr Schiff – a decision under the sole control of Ms Pelosi – Mr Hoyer made clear on Thursday he was not going anywhere.

"Let me assure the gentleman, there is not a person on my side of the aisle that believes that Mr Schiff has done anything but act in the highest interest of our government, of the Intelligence Committee, and of full knowledge for the American people," he said.