Meanwhile, US President Donald Trump's former national security advisor John Bolton has been asked to testify in the impeachment probe examining potential abuse of power by the president, US media reported.
Democrats set the stage Wednesday for certain House approval of the ground rules lawmakers will use when they consider impeaching President Donald Trump as the chamber braced for its first showdown over the inquiry.
There was no doubt that the Democratic-controlled body would approve the eight pages of procedures on Thursday, with each side likely to lose a handful of defectors, if any.
"As much as this president flaunts the Constitution, we are going to protect it," House Rules Committee Chairman James McGovern, D-Mass., said as his panel debated the procedures.
House Minority Leader Kevin McCarthy told The Associated Press that the package creates "much more of a politically closed system than an open system."
That echoed Republican complaints that the Democratic-run process has been secretive and tilted against them. Democrats say their plan follows how impeachment efforts against Presidents Richard Nixon and Bill Clinton were run.
TRT World's Jon Brain has more.
John Bolton to testify
Trump's former national security advisor John Bolton has been asked to testify in the impeachment probe examining potential abuse of power by the president, US media reported Wednesday.
Bolton, who resigned in September, has been called on to testify behind closed doors on November 7, The Washington Post reported, as the White House seeks to limit cooperation with the probe by current and former administration officials.
Bolton was reported to have expressed alarm over secret administration efforts, including by Trump's personal attorney Rudy Giuliani, to pressure Ukraine to investigate Democrats including potential Trump presidential rival Joe Biden.
Bolton's lawyer and Democratic aides did not respond to requests for comment on the testimony notice or say whether Bolton had agreed to appear before investigators.
The investigation is focused on Trump's efforts to push Ukraine to investigate his Democratic political opponents by withholding military aid and an Oval Office meeting craved by the country's new president.
It is likely to take weeks or more before the House votes on whether to actually impeach Trump. If the House impeaches Trump, the Senate would hold a trial to decide whether to remove him from office.
Both parties' leaders were rounding up votes as Thursday's roll call approached, with each side eager to come as close to unanimity as possible.
Republicans said a solid GOP "no" vote would signal to the Senate that the Democratic push is a partisan crusade against a president they have never liked. McCarthy, R-Calif., said he's unaware of any Republican even "leaning toward voting for it."
Rep. Fred Upton, R-Mich., a moderate who some thought might be open to backing the Democratic rules, said he would oppose them. He complained about the secrecy that Democrats have used and said he had not been pressured by GOP leaders or Trump, with whom he had a drink at a Republican fundraiser Tuesday night.
"You really can't roll back the clock" from the time the investigation began last month, Upton said.
Democrats were also hoping to demonstrate solidarity from their most liberal elements to their most moderate members. They argued that GOP cohesion against the measure would show that Republicans are blindly defending Trump, whatever facts emerge.
"It will show the other party has become the party of Trump. It's really not the Republican Party any longer," said Rep. Dan Kildee, D-Mich.
Democrats' chief vote counter, Rep. James Clyburn of South Carolina, said he believed "less than half a dozen" from his party would oppose the package. One Democrat whose vote was unclear, New York freshman Rep. Anthony Brindisi, said he'd not been pressured by party leaders to back the measure and said, "This is a decision I have to make."
Republicans said they'd use the vote to target freshman Democrats and those from districts Trump carried in 2016. They said they would contrast their support for the rules with campaign promises to focus on issues voters want to address, not on impeaching Trump.
The House GOP's campaign arm sent emails to reporters all but taunting some of those Democrats including freshman Rep. Chris Pappas, D-N.H. "Pappas wants to be a one-termer," one said.
GOP leaders called the rules "Speaker Pelosi's sham process designed to discredit the Democratic process" in their daily impeachment email to lawmakers.
House Speaker Nancy Pelosi, D-Calif., decided to have the vote following weeks of GOP claims that the inquiry was invalid because the chamber had not voted to formally commence the work.
The rules lay out how the House Intelligence Committee — now leading the investigation by deposing diplomats and other officials behind closed doors — would transition to public hearings.
That panel would issue a report and release transcripts of the closed-door interviews it has been conducting with diplomats and other officials with connections to Trump's interactions with Ukraine.
The Judiciary Committee would then decide whether to recommend that the House impeach Trump — a finding that he should be removed from office.
Republicans could only issue subpoenas for witnesses to appear if the entire panel approved them — in effect giving Democrats veto power over such requests by the GOP.
Attorneys for Trump could participate in the Judiciary Committee proceedings. But in a bid for leverage, panel Chairman Jerrold Nadler, D-N.Y., would be allowed to deny "specific requests" by Trump representatives if the White House continue s refusing to provide documents or witnesses sought by Democratic investigators.
The rules also direct House committees "to continue their ongoing investigations" of Trump.
Top Democrats think that language will shield their members from weeks of Republican complaints that the inquiry has been invalid because the House had not formally voted to begin that work.
Democrats have said there is no constitutional provision or House rule requiring such a vote.