President Trump, in an exclusive wide-ranging interview Wednesday night with Fox News' "Hannity," vowed to release the full and unredacted Foreign Intelligence Surveillance Act (FISA) warrants and related documents used by the FBI to probe his campaign, saying he wants to "get to the bottom" of how the long-running Russia collusion narrative began.

Trump told anchor Sean Hannity that his lawyers previously had advised him not to take that dramatic step out of fear that it could be considered obstruction of justice.

"I do, I have plans to declassify and release. I have plans to absolutely release," Trump said. "I have some very talented people working for me, lawyers, and they really didn't want me to do it early on. ... A lot of people wanted me to do it a long time ago. I'm glad I didn't do it. We got a great result without having to do it, but we will. One of the reasons that my lawyers didn't want me to do it, is they said, if I do it, they'll call it a form of obstruction."

Trump added: "Frankly, thought it would be better if we held it to the end. But at the right time, we will be absolutely releasing."

Trump also accused FBI officials of committing "treason" -- slamming former FBI Director James Comey as a "terrible guy," former CIA Director John Brennan as potentially mentally ill, and Democrat House Intelligence Committee Chairman Adam Schiff as a criminal.

Redacted versions of FISA documents already released have revealed that the FBI extensively relied on documents produced by Christopher Steele, an anti-Trump British ex-spy working for a firm funded by the Hillary Clinton campaign and Democratic National Committee, to surveil Trump aide Carter Page. At least one senior DOJ official had apparent concerns Steele was unreliable, according to text messages exclusively obtained last week by Fox News.

The leaked dossier, and related FBI surveillance, kickstarted a media frenzy on alleged Russia-Trump collusion that ended with a whimper on Sunday, when it was revealed Special Counsel Robert Mueller's probe concluded finding no evidence of such a conspiracy, despite several offers by Russians to help the Trump campaign. Page was never charged with wrongdoing, and he is currently suing the DNC for defamation.

FOX NEWS EXCLUSIVE: NEWLY REVEALED TEXTS SHOW DOJ OFFICIALS CLASHING WITH FBI OVER 'BIAS' OF KEY WARRANT SOURCE

Citing a high-level source, Kentucky GOP Sen. Rand Paul late Wednesday tweeted that anti-Trump ex-CIA Director John Brennan had internally pushed the dossier. Fox News has not independently verified Paul's source.

"I think Brennan's a sick person, I really do," Trump said. "I believe there's something wrong with him, for him to come out of the CIA and act that way was so disrespectful to the country and to the CIA. He was not considered good at what he did. He was never a respected guy."

Brennan was one of the loudest and most virulent voices to trumpet the Russian collusion theory over the past two years, asserting falsely just weeks ago that Mueller was likely planning to indict members of the Trump administration's family in a scene reminiscent of the "ides of March” and the assassination of Julius Caesar. Trump, who revoked Brennan's security clearance last year amid concerns Brennan was improperly hinting that he had inside information about ongoing federal probes, called those remarks "horrible" on Wednesday.

Brennan has since acknowledged he was wrong, but has said inaccurately that Mueller merely could not find evidence meeting the high bar needed for a criminal prosecution -- when in fact Mueller found no evidence at all that the Trump team responded to Russians' numerous efforts to involve them in a conspiracy.

"When I said there could be somebody spying on my campaign, it went wild out there," Trump told Hannity. "They couldn't believe I could say such a thing. As it turned out, that was small potatoes compared to what went on. ... Millions and millions [spent] on the phony dossier, and then they used the dossier to start things. It was a fraud, paid for by Hillary Clinton and the Democrats."

Just hours earlier Wednesday, Trump made clear he was enthusiastic about the idea of appointing a second special counsel to review the origins of the Russia investigation when it came up during a meeting Tuesday with Republican senators, a source familiar with the discussions told Fox News.

Trump, speaking to Hannity, separately raised doubts about the secretive and mysterious June 27, 2016 Phoenix airport tarmac meeting between Bill Clinton and then-Attorney General Loretta Lynch -- which was spotted while Lynch was overseeing the Hillary Clinton email probe.

"I had a lot of planes for a long time. I’ve never stopped the plane on the tarmac to let somebody on the plane," Trump said. "Bill Clinton said he was there to play golf, but I know the area very well. Arizona. It's a little warm at that time of year for golf, OK?"

RAND PAUL BOMBSHELL: HIGH-LEVEL SOURCE SAYS BRENNAN PUSHED DISCREDITED ANTI-TRUMP STEELE DOSSIER

In an apparent shot at former Attorney General Jeff Sessions, Trump also told Hannity "this all would not have happened" if Attorney General William Barr had been with his administration from the beginning.

Trump also noted that ratings for several networks that aggressively pushed the Russia narrative have "fallen off" dramatically. MSNBC host Rachel Maddow's audience of 2.5 million on Monday was 19 percent below her average this year, and it went down further to 2.3 million on Tuesday, according to the Nielsen company.

"If you wrote this as a novel, nobody would buy it; it would be a failure, because it would be too unbelievable," Trump said. "We're getting to the bottom of it. This can never, ever happen to a president again. That was a disgrace and an embarrassment to our country. ... Hopefully they won't get away with it.

"We'll have to see how it all started, but I'm going to leave that to other people, including the attorney general and others, to make that determination," Trump continued. "Fifty years, 100 years from now -- if someone tries the same thing, they have to know the penalty will be very very great if and when they get caught."

Trump also lashed out at Schiff, D-Calif., who has pushed strongly for investigations into possible Trump-Russia links. "Schiff is a bad guy, he knew he was lying -- he's not a dummy. For a year and a half he would just leak and call up CNN and others. You know, I watch him, so sanctimonious ... He knew it was a lie, and he'd get in the back room with his friends in the Democrat Party, and they would laugh like hell. In one way, you could say it's a crime what he did -- he was making statements he knew were false. He's a disgrace to our country."

The president insisted the U.S. should have a "great relationship" with Russia and China, but that the "fake news" and "nonsense" distorted his intentions into something more sinister.

Trump also criticized Comey, whom he'd fired in 2017, as a "terrible guy." He insisted he did not fire him to obstruct justice, telling Hannity he knew that firing Comey would only increase scrutiny on the White House.

"It was treason, it was really treason," Trump said, referring to texts between former FBI Special Agent Peter Strzok and former FBI lawyer Lisa Page that discussed an "insurance policy" in the event of Trump's election.

"You had dirty cops, you had people who are bad FBI folks ... At the top, they were not clean, to put it mildly." He said later, "We can never allow these treasonous acts to happen to another president."

"I do, I have plans to declassify and release." — President Trump

Separately, Trump also said he hopes Democrats continue pushing the Green New Deal, which flamed out in a test vote on Tuesday, as most Democrats voted "present" instead of going on record supporting the sweeping transformation of the entire U.S. economy.

"I don't want to speak badly about the New Green Deal, frankly, because I’m afraid they will stop using it," Trump said. "I really do want to campaign against it. It's ridiculous."

Trump's interview came as multiple GOP lawmakers have claimed the president may have somewhat undercut perhaps the best week of his presidency by backing the complete overturn of ObamaCare.

On Monday, the Justice Department asked the U.S. Court of Appeals for the Fifth Circuit in New Orleans to affirm last year's ruling by a Texas federal judge stating that the Affordable Care Act was no longer constitutional because the 2017 tax reform legislation eliminated the health care law’s penalty for not having health insurance.

Multiple congressional Republicans told Fox News they were bothered by the timing of the Trump administration's intervention in the matter, which came on the heels of the Mueller report findings, the House sustaining the president's veto of a bill to halt the national emergency for the border wall and a Senate vote that shined a spotlight on what conservatives described as problems with the Green New Deal, championed by Rep. Alexandria Ocasio-Cortez, D-N.Y.

Trump, despite the pushback, vowed that Republicans would soon be the "party of great health care."

Fox News' Catherine Herridge contributed to this report.