President Donald Trump on Sunday took out his frustrations over the intensifying Russia investigation by lashing out at special counsel Robert Mueller, signaling a possible shift away from a strategy of cooperating with a probe he believes is biased against him.

In a series of weekend tweets naming Mueller for the first time, Trump criticized the investigation into Russian interference in the 2016 presidential election and raised fresh concerns about the objectivity and political leanings of the members of Mueller’s team.

Trump also challenged the honesty of Andrew McCabe, the newly fired FBI deputy director, and James Comey, the bureau’s former director whom Trump fired last year over the Russia probe.

The president’s aggressive stance followed a call Saturday by his personal lawyer for Rod Rosenstein, whom Trump appointed as deputy attorney general and who now oversees Mueller’s inquiry, to “bring an end” to that investigation.

Republicans on the House Intelligence Committee, which spent the past year conducting a parallel investigation, recently said they had drafted a report concluding no collusion or coordination between Trump’s presidential campaign and Russia. Committee Democrats vehemently disagreed.

“The Mueller probe should never have been started in that there was no collusion and there was no crime,” Trump tweeted Saturday. “It was based on fraudulent activities and a Fake Dossier paid for by Crooked Hillary and the DNC, and improperly used in FISA COURT for surveillance of my campaign. WITCH HUNT!” Trump was referring to a dossier of anti-Trump research funded by the Democratic Party and Hillary Clinton’s campaign.

Likely adding to Trump’s growing frustration, The New York Times reported last week that Mueller had subpoenaed the Trump Organization and requested Russia-related documents. Trump had said Mueller would cross a red line with such a step.

“Why does the Mueller team have 13 hardened Democrats, some big Crooked Hillary supporters, and Zero Republicans?” Trump tweeted Sunday.

Some of Mueller’s investigators indeed have contributed to Democratic political candidates, but Justice Department policy and federal service law bar discrimination in the hiring of career positions on the basis of political affiliation. Mueller is a Republican.

Trump’s attacks raised new concerns among members of Congress that he could be seeking to orchestrate Mueller’s firing. Republican and Democratic lawmakers warned Trump to not even think about it.

“If he tried to do that, that would be the beginning of the end of his presidency,” said Sen. Lindsey Graham, R-S.C., a Trump ally.

Sen. Dick Durbin, D-Ill., called for the passage of bipartisan bills designed to protect Mueller that have stalled in Congress.

“This president is engaged in desperate and reckless conduct to intimidate his law enforcement agencies of this country and to try and stop the special counsel. That is unacceptable in a democracy,” Durbin said.

Trump cannot directly fire Mueller, who can only be dismissed for cause. Any dismissal of Mueller would have to be carried out by Rosenstein, who has publicly expressed his support for Mueller.

Aides and friends say they understand Trump’s frustration with an investigation that hangs over his presidency.

“When he says it’s a political witch hunt, I think he’s right,” said Christopher Ruddy, CEO of the conservative news website Newsmax and a longtime Trump friend.

Marc Short, Trump’s congressional liaison, said the president’s frustration is “well-warranted” because “there has been no evidence whatsoever of collusion.”

Trump may have felt emboldened after Attorney General Jeff Sessions fired McCabe on Friday. “A great day for Democracy,” Trump tweeted afterward. Trump asserted without elaboration that McCabe, whose firing he had publicly called for, knew “all about the lies and corruption going on at the highest levels of the FBI!”

The Associated Press later reported that McCabe kept personal memos detailing interactions with Trump that have been provided to Mueller’s office and are similar to notes compiled by Comey. Trump sought to cast doubt on their veracity.

“Spent very little time with Andrew McCabe, but he never took notes when he was with me,” Trump tweeted Sunday. “I don’t believe he made memos except to help his own agenda, probably at a later date. Same with lying James Comey. Can we call them Fake Memos?”

It wouldn’t be unusual for a senior official to make notes soon after meeting with the president.

Trump also claimed Comey lied under oath at a Senate hearing by saying he had never been an anonymous source. Comey, who is releasing a book next month, tweeted Saturday after McCabe’s firing: “Mr. President, the American people will hear my story very soon. And they can judge for themselves who is honorable and who is not.”

The contents of McCabe’s memos are unknown, but they could help substantiate McCabe’s assertion that he was unfairly maligned by a White House he says had declared “war” on the FBI and Mueller’s investigation.

Sessions said he dismissed McCabe on the recommendation of FBI disciplinary officials who said McCabe had not been candid with a watchdog office investigation. An upcoming inspector general’s report is expected to conclude that McCabe had authorized the release of information to the media and was not forthcoming with the watchdog office as it examined the bureau’s handling of an investigation into Clinton’s emails.

McCabe has vigorously disputed the allegations and said his credibility had been attacked as “part of a larger effort not just to slander me personally” but also the FBI and law enforcement.

Also over the weekend, Trump’s personal lawyer, John Dowd, cited the “brilliant and courageous example” by Sessions and the FBI’s Office of Professional Responsibility and said Rosenstein should “bring an end” to the Russia investigation “manufactured” by Comey.

In response, Rep. Trey Gowdy, R-S.C., said: “If you have an innocent client, Mr. Dowd, act like it.”

Dowd told the AP that he wasn’t calling on Rosenstein to fire the special counsel immediately and hadn’t discussed with him the idea of dismissing Mueller or ending the probe. Dowd also said he was speaking for himself and not the president.

Mueller is investigating whether Trump’s actions, including Comey’s ouster, constitute obstruction of justice.

(AP)