The chairman of the House Intelligence Committee said Wednesday he has seen no evidence backing up President Donald Trump’s allegation the administration of former President Barack Obama wiretapped Trump’s personal offices in New York City before the November election.

“We don't have any evidence that that took place,” Rep. Devin Nunes, R-Calif., told reporters at a news conference in Washington. “I don't think there was an actual tap of Trump Tower.”

It was “obvious” that Obama didn’t personally implore his national security advisers to install listening devices inside Trump Tower, where Trump's primary office and residence are, Nunes said.

Read: Just Kidding? Trump Spokesman Rolls Back Obama Wiretapping Claim

“If the White House or the president want to come out and clarify his statements more, it would probably, probably be helpful,” Nunes said, in reference to the president’s March 4 tweets, where he called Obama "sick" for ordering the alleged wiretaps.

It was unclear on what Trump based his tweetstorm. Speculation centered on a conspiracy theory proffered on the alt-right website Breitbart News. 

FBI Director James Comey is scheduled to testify publicly before the committee Monday and will be questioned about Trump's wiretap claims in addition to whether the FBI had any information regarding members of the Trump team meeting with Russian government officials during the presidential election, USA Today reported Wednesday. 

Sen. Lindsey Graham, R-S.C., a senior member of the Senate Judiciary Committee, threatened Wednesday to subpoena Comey if he failed to answer whether the FBI received a federal warrant to conduct surveillance on Trump, his campaign or his Manhattan headquarters. 

Sean Spicer, the White House press secretary, insisted Monday there were numerous reports from a “variety of outlets over the last couple months that seemed to indicate that there has been some kind of surveillance that occurred during the 2016 election," but at the same time softening Trump's allegation by explaining Trump didn't think Obama installed the alleged wiretaps personally.

Senior White House adviser Kellyanne Conway contentiously said in an interview Sunday the federal government had several means of spying on Trump aside from a traditional wiretap, suggesting that the Obama administration could have snooped on Trump’s conversations via several electrical appliances like microwaves. Subsequent reports revealed there are no microwaves manufactured with listening devices incorporated.