Democrats in the US Congress have debated possibly impeaching Republican President Donald Trump.

As Democrats in the U.S. Congress debated possibly impeaching Republican President Donald Trump, House Speaker Nancy Pelosi said on Wednesday, about an hour before a White House meeting with him, that Trump is engaged in a "cover-up."

The president is stonewalling multiple congressional investigations by ignoring subpoenas, refusing to allow current and former advisers to testify, and not handing over documents, steps that have aggravated a confrontation with Congress.

"No one is above the law, including the president of the United States. And we believe that the president of the United States is engaged in a cover-up," Pelosi told reporters after a morning meeting of House of Representatives Democrats.

She and other congressional leaders were scheduled to meet midmorning at the White House with Trump to talk about a potential bipartisan infrastructure development plan, although a firm proposal for funding any such effort has yet to emerge.

It was unclear if the meeting would occur after Trump wrote on Twitter about the time it was to begin: "As I have long been saying, and has now been proven out, this is a Witch Hunt against the Republican Party and myself, and it was the other side that caused the problem, not us!"

Trump and Democrats who control the House are engaged in a high-stakes power struggle over their ability to investigate him, with the president increasingly asserting that his advisers need not respond to lawmakers' inquiries.

Their probes range from whether Trump obstructed justice during Special Counsel Robert Mueller's inquiry into Russian meddling in Trump's favor in the 2016 U.S. presidential election to his personal finances and businesses.

As the confrontation has escalated, Pelosi and other senior House leaders have been trying to tamp down demands from more junior Democratic lawmakers to kick off impeachment proceedings, urging them to give court enforcement actions time to progress.

The Democratic chairman of the House Intelligence Committee said on Wednesday he would hold off enforcing a subpoena against Attorney General William Barr after the Justice Department agreed to turn over materials relating to an investigation into Russian election interference.

The decision ended a standoff between the committee and the Justice Department for access to counterintelligence reports generated by Mueller during his probe.

"The Department of Justice has accepted our offer of a first step towards compliance with our subpoena, and this week will begin turning over to the committee twelve categories of counterintelligence and foreign intelligence materials as part of an initial rolling production," Committee Chairman Adam Schiff said in a statement on Wednesday.

Several House Democrats left Wednesday morning's meeting telling reporters that Schiff's deal might cool some of the passion for immediately moving toward impeachment

But impeachment demands have mounted since former White House Counsel Don McGahn ignored a subpoena from the House Judiciary Committee on Tuesday to appear before it and testify.

"For many of us, we think at least an impeachment inquiry would give us more ability to get witnesses to come to Congress. We're just trying to figure out how to get the truth," Democratic Representative Mark Pocan told MSNBC.

Democratic Representative Gerry Connolly told reporters that Pelosi was working to balance the demands of Democrats in the House. But he added, "I am increasingly concerned that this president has committed impeachable offenses."