WASHINGTON (Reuters) - The top Democrat on the U.S. House Intelligence Committee described on Wednesday “a developing pattern” in which witnesses have declined to discuss events occurring after President Donald Trump’s election in the panel’s probe of Russia and the 2016 vote.

Rep. Adam Schiff, the ranking Democratic member on the House Intelligence Committee, arrives to watch U.S. President Donald Trump deliver his State of the Union address to a joint session of the U.S. Congress on Capitol Hill in Washington, U.S. January 30, 2018. REUTERS/Joshua Roberts

“Some witnesses have been postponed, others canceled, and two specifically have refused to answer questions about the events in the period,” Representative Adam Schiff said in a statement.

He called it “a developing pattern” over the past several weeks.

On Tuesday, Schiff said the committee should begin contempt proceedings if Steve Bannon, a former senior Trump adviser, continued to refuse to testify, after Bannon did not comply with a subpoena. Schiff said the White House limited his testimony to a pre-approved set of 14 questions.

Bannon is now expected to appear before the House of Representatives committee next week.

Schiff said the committee was informed on Tuesday that Corey Lewandowski, a former Trump campaign manager, would refuse to reappear before the committee to testify any further, despite agreeing earlier to do so.

White House officials and attorneys for Bannon or Lewandowski did not respond to requests for comment.

Schiff said that neither Bannon nor Lewandowski had given “legitimate” reasons for refusing to appear, and that they were expected to return.

“It will therefore be necessary for our Committee to enforce the subpoena on Bannon, and now move to compel Lewandowski’s testimony, among other outstanding steps needed to advance the investigation,” Schiff said.

House Intelligence is one of three congressional committees investigating Russia and the 2016 U.S. election, after U.S. intelligence agencies found that Russia attempted to influence the campaign on Trump’s behalf.

Special Counsel Robert Mueller is also investigating.

Moscow has denied meddling in the U.S. presidential election, and Trump denied any collusion between his associates and Moscow.