President Donald Trump (C) shakes hands with James Comey, director of the Federal Bureau of Investigation (FBI), during an Inaugural Law Enforcement Officers and First Responders Reception in the Blue Room of the White House on January 22, 2017 in Washington, DC.

U.S. President Donald Trump insists he "won't be involved" in any attempt to interfere with the investigation into Russian election meddling — unless he changes his mind.

Trump also is renewing his attacks on James Comey, the FBI director he fired last year, accusing him of lying about Trump's trip to Moscow in 2013 that has received fresh scrutiny. Early Friday, Trump accused Comey in a tweet of leaking classified information.

"He's either very sick or very dumb," Trump tweeted.

Donald Trump tweet

On Thursday, the GOP-led Senate Judiciary Committee approved a measure that would safeguard special counsel Robert Mueller from being fired. The move came shortly after Trump, in a television interview, blasted the Justice Department, which oversees the special counsel's investigation.

"I am very disappointed in my Justice Department. But because of the fact that it's going on, and I think you'll understand this, I have decided that I won't be involved," the president said in a telephone interview with "Fox & Friends."

But then he added: "I may change my mind at some point, because what's going on is a disgrace."

The Mueller legislation approved by the Senate panel may be largely symbolic, since Majority Leader Mitch McConnell has said he won't bring it up for a full Senate vote. But it shows there are limits to Republican support for Trump when it comes to the president's attacks on the special counsel's probe.

Four Republicans joined Democrats in a 14-7 committee vote to approve the measure.

Nearly all GOP senators say Trump shouldn't fire Mueller. And Republicans who support the legislation say it's necessary to guard against presidential interference by giving Congress more oversight power.

"While my constitutional concerns remain, I believe this bill should be considered by the full Senate," said Sen. Chuck Grassley, R-Iowa, chairman of the committee, adding to pressure on McConnell.

Trump has increased his criticism of the Russia investigation since the FBI's raids on the office and hotel room being used by Michael Cohen, a Trump personal attorney who is under federal criminal investigation in New York for unspecified business dealings.

Trump again called the investigation "a witch hunt" and insisted there was "no collusion" with Russia. Much of his vitriol in his TV remarks was directed at Comey.

He laced into the former FBI director as "a leaker" and "a liar." He disputed Comey's claim that Trump told him he did not spend the night in Moscow during his 2013 trip to attend the Miss Universe pageant.

"He said I didn't stay there a night. Of course I stayed there," Trump said. "I stayed there a very short period of time but of course I stayed."

Comey last year created a series of contemporaneous memos — some classified, some not — to document his interactions with Trump. He wrote in the memos that Trump repeatedly brought up allegations contained in an unverified document that explored ties between Trump's orbit and Russia.

Among the most salacious details was a report that Trump consorted with prostitutes overnight on that trip, a claim Trump has denied. Comey wrote in the memos that Trump told him that he'd never stayed the night in Moscow.

Flight records and social media posts from that week indicate that Trump did spend at least one night in Russia. Comey said on a CNN program that aired Wednesday — watched by Trump — that he was always concerned when someone lied to the FBI, particularly if it was about something that an agent never asked about, as he said was the case with Trump.

"It tends to reflect consciousness of guilt as we would say in law enforcement," Comey said. He added: "If they bring things up you didn't ask about, and if they bring it up and make a false statement about it, that's — it's not definitive, but it certainly makes you very concerned about what might be going on there."

Trump denied having that conversation with Comey.

"You look at the corruption at the top of the FBI. It's a disgrace," Trump said. "And our Justice Department, which I try and stay away from, but at some point I won't."

He also suggested Comey leaked classified information in the memos.

Comey has denied that allegation. He has acknowledged that the Justice Department's inspector general, who has been investigating FBI actions during the Hillary Clinton email probe, was examining whether Comey complied with FBI policy in how he produced and stored the memos. He said that inquiry is not looking at whether he mishandled classified information, "because that's frivolous."

"The bottom line is, I see no credible claim by any serious person that that violated the law," he said on CNN.

A conscious effort by Trump to mislead the FBI director could lend weight to the allegation, contained in the private research dossier compiled by a former British spy in 2016, that Trump engaged in compromising activity during the trip that exposed him to potential Russian blackmail.

The Mueller probe has already led to the indictments of several former Trump campaign officials, including onetime campaign chairman Paul Manafort, who is charged with engaging in conspiracy and money laundering. Trump, who recently added former New York City Mayor Rudy Giuliani to his legal team, has not committed to sitting for an interview with Mueller's investigators.