Washington (CNN) Senate Minority Leader Chuck Schumer said on Sunday that President Donald Trump should not voice his concerns about the impeachment hearings on Twitter but instead should appear before Congress to testify.

The New York Democrat's comments follow the first public hearings in the House impeachment inquiry into the President and Ukraine. Trump has continuously tweeted arguments in his own defense and lashed out at Democrats about the probe, calling it a "witch hunt."

A number of former and current Trump administration officials have defied subpoenas seeking testimony before the House Intelligence Committee, and in some cases the White House has instructed administration officials to assert executive privilege.

"I think the hearings have brought up many, many troubling allegations. And this morning (House) Speaker (Nancy) Pelosi invited President Trump to come testify, and I think her invitation is correct. If Donald Trump doesn't agree with what he's hearing, doesn't like what he's hearing, he shouldn't tweet. He should come to the committee and testify under oath and he should allow all those around him to come to the committee and testify under oath," Schumer said at an unrelated news conference in New York City.

He continued: "When Donald Trump refuses to come to the committee, now that Speaker Pelosi has invited him, when he doesn't let all the people around him come before the committee, you've got to ask the question: What is he hiding? What is he afraid to confront what these people have said?"

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