Trump is acting like a cornered animal on Twitter this morning: What about Clinton and the Russians?
Donald Trump speaking with supporters at a campaign rally at the Prescott Valley Event Center in Prescott Valley, Arizona (Gage Skidmore/Flickr)

President Donald Trump lashed out Monday morning on Twitter ahead of the FBI director's testimony before a House panel on his campaign's alleged ties to Russia.

The president started tweeting at 6:35 a.m. by denouncing the allegations, which are under investigation by the House Intelligence Committee, as "fake news."

WATCH LIVE: FBI Director James Comey testifies about Russia before the House Intelligence Committee

Clapper, the former director of national intelligence, has said he found no evidence of collusion between Trump's campaign and Russia, but the committee's ranking Democrat said Sunday that circumstantial evidence suggested collusion and direct evidence showed deception.

FBI Director James Comey is expected to address Trump's allegations that his predecessor, Barack Obama, ordered a wiretap of Trump Tower during the campaign, which various Republican and Democratic officials have dismissed as unfounded.

Trump also criticized CNN for reporting on a Gallup poll showing a record low 37 percent approval rating and 58 percent disapproval after just 60 days on the job.

He also cited claims by Russian President Vladimir Putin's spokesman, Dmitry Peskov, who said “people working in think tanks advising Hillary or advising people working for Hillary” met with Russian ambassador Sergey Kislyak.

Trump's national security adviser, Mike Flynn, stepped down after lying about his meetings with Kislyak, and Attorney General Jeff Sessions also failed to disclose his own meetings with the ambassador during his confirmation hearings.

Peskov pointed out that Putin had not endorsed a candidate for U.S. president, but he conceded the Russian president preferred Trump over Clinton.