WASHINGTON -- President Trump is calling the investigations of his campaign’s ties with Russia a “hoax” -- even though his national security adviser and his campaign chairman were fired over it.

The House, the Senate and the FBI are looking into Russian meddling in the election.

Tuesday, the Republican chairman of the House Intelligence Committee said he will not take himself off the investigation.

Democrats and at least one Republican are demanding Rep. Devin Nunes, R-Calif., recuse himself because he has appeared to be coordinating with the White House.

“Are you going to stay as chairman of this investigation,” a reporter asks Nunes on Tuesday. “Why would I not?” he said.

Nunes dismissed accusations he has been intentionally delaying his committee’s investigation.

The committee has held one public hearing on Russia and was supposed to have a second Tuesday. But after Nunes announced late last week that he had been shown intercepted communications involving members of the Trump transition team, the Tuesday’s session was canceled.

It was supposed to feature testimony from former acting Attorney General Sally Yates about the Justice Department’s investigation of former National Security Advisor Michael Flynn. In January, Yates informed the White House that Flynn had misled the vice president about his contacts with the Russian ambassador.

CBS News obtained a letter from the Trump Justice Department to Yates’ attorney warning that there was a limit to what she could reveal in her testimony and that “she needs to consult with the White House.”

CBS News obtained a letter from former acting Attorney General Sally Yates. CBS Evening News

Yates followed up with White House lawyers on Friday. They never responded, and the same day -- Nunes canceled the hearing.

White House press secretary Sean Spicer said, technically, the White House didn’t stop her testimony.

“The White House did not respond and took no action that prevented Ms. Yates from testifying,” Spicer said at a White House press briefing.

“Right now I should be sitting in a hearing and the American people should be hearing from Sally Yates,” Rep. Eric Swalwell, D-Calif., said.

Swalwell is a member of the House Intelligence Committee and spoke with CBS News.

“This is what cover-up behavior looks like,” he said. “And it’s our job to get to the bottom of what’s going on, but right now the American people want transparency, and what they are getting are more and more smoke bombs.”

While some Republicans have been critical on Rep. Nunes, only one GOP member of the House has joined Democrats in calling for him to step aside. Tuesday, Rep. Walter Jones, R-North Carolina, broke ranks and said Nunes should recuse himself.