During an interview on Wednesday, Fox News' Tucker Carlson grilled President Donald Trump over his explosive wiretapping allegations leveled against President Barack Obama, asking why Trump couldn't gather the evidence himself, if such evidence existed, when "every intelligence agency reports to you."

Trump tweeted earlier this month, without presenting evidence, that Obama had Trump Tower's "wires tapped" during the presidential campaign.

"Fifty-one thousand people retweeted that," Carlson said. "So a lot of people thought that was plausible. They believe you. You're the president — you're in charge of the agencies. Every intelligence agency reports to you. Why not immediately go to them and gather evidence to support that?"

The White House released a statement shortly after Trump leveled the accusations "requesting that ... the congressional intelligence committees exercise their oversight authority to determine whether executive branch investigative powers were abused in 2016."

Many experts have said, however, that Trump could find out immediately if a warrant had been obtained by the Obama administration to surveil Trump Tower. There is no indication that the White House has directly asked the FBI whether that warrant exists.

Trump told Carlson that he didn't "want to do anything that's going to violate any strength of an agency."

"We have enough problems," he said. "We will be submitting certain things, and I will be perhaps speaking about this next week, but it's right now before the committee, and I think I want to leave it. I have a lot of confidence in the committee."

The chairman of the House Intelligence Committee, Rep. Devin Nunes of California, on Wednesday said the committee had not found any evidence to support Trump's claim that Obama had Trump Tower's phones tapped.

Carlson doubled down, asking why Trump wouldn't have waited "to tweet about it until you can prove it."

"Don't you devalue your words when you can't provide evidence?" Carlson asked.

Trump said he tweeted the accusation because he had read about wiretapping in The New York Times and heard Fox News anchor Bret Baier "mention the word 'wiretap.'"

"Well, because The New York Times wrote about it," Trump said. "Not that I respect The New York Times. I call it the 'failing New York Times.' But they did write on January 20 using the word 'wiretap.'"

The New York Times reported on January 19 that the FBI, the National Security Agency, and the CIA were investigating possible links between Trump associates and Russian officials based partly on intercepted communications that had been obtained via wiretapping. The Times did not report that Obama had ordered the wiretapping, or that the wiretapping had directly targeted Trump associates.

Instead, Trump's tweets appeared to have been based largely on a Breitbart article that had been placed in his reading pile before he tweeted. The article based its claims on a theory floated by the conservative radio host Mark Levin that Obama had mounted a "silent coup" against Trump using "police state" tactics that included wiretapping.

Carlson again told Trump that he was the president and therefore had "the ability to gather all the evidence" he wanted.

"I do. I do. But I think that, frankly, we have a lot right now," Trump said. "And I think if you watch — if you watched Bret Baier and what he was saying, and what he was talking about, and how he mentioned the word 'wiretap,' you would feel very confident that you could mention the name. He mentioned it. And other people have mentioned it."

Trump said that in the tweet, the words "wires tapped" were in quotes. White House press secretary Sean Spicer said last week that Trump meant the Obama administration had been surveilling him generally, not that "President Obama went up and tapped his phone personally."

"Don't forget, when I say wiretapping, those words were in quotes," Trump told Carlson. "That really covers — because wiretapping is pretty old-fashioned stuff, but that really covers surveillance and many other things. And nobody ever talks about the fact that it was in quotes, but that's a very important thing. But wiretap covers a lot of different things. I think you're going to find some very interesting items coming to the forefront over the next two weeks."

Rep. Adam Schiff, the ranking Democrat on the House Intelligence Committee, said Wednesday that he had "seen no evidence of illegality of any electronic surveillance" and that "there was no substance to the accusation that President Obama wiretapped Trump Tower."

Nunes, the House intelligence chair, said FBI Director James Comey had still not told the committee directly whether the bureau had sought and obtained a warrant under the Foreign Intelligence Surveillance Act to surveil anyone who might have communicated with Trump associates during the campaign. Nunes said Comey had agreed to testify at a public House Intelligence Committee hearing next week about the FBI's investigation into Russia's meddling in the 2016 election.

The FBI also briefed the Senate Judiciary Committee on Wednesday afternoon.

Republican Sen. Lindsey Graham, the chair of the Senate Judiciary Committee's subcommittee on crime and terrorism, told the FBI on Tuesday that it would "screw up big time" if it failed to respond to his subcommittee's letter asking for "copies of any warrant applications and court orders" related to any wiretaps of Trump.