A top Democratic impeachment prosecutor has suggested that he would widen a House probe against President Donald Trump even if he is acquitted by the Senate.
New York Congressman Jerry Nadler said the House was “likely” to subpoena former Trump aide John Bolton for testimony.
Mr Bolton could face questions beyond the impeachment articles, he said.
If he testifies, “we’re talking about everything,” Mr Nadler told reporters.
The comments came hours before the Senate was expected to vote against removing Mr Trump from office.
Mr Trump is charged with abuse of power and obstruction of Congress. He is accused of withholding military aide to Ukraine to press Kyiv for an investigation into Joe Biden, a Democratic rival.
A manuscript of a forthcoming book by Mr Bolton reportedly claims that Mr Trump told the former national security advisor to help in the campaign.
The claim is the only time the president has been directly linked to the alleged scheme, but the Senate rejected a vote to hear from Mr Bolton as a witness.
Mr Nadler, the chairman of the House Judiciary Committee, told reporters on Wednesday that “it’s likely” Mr Bolton will be subpoenaed by the lower chamber, even if the Senate votes to acquit the president.
Mr Nadler said that Ukraine would not be the only topic asked of Mr Bolton if he testifies.
Democrats in the House had previously sought Mr Bolton’s testimony, but he declined to appear after the White House refused to allow any current or former aides to co-operate with the investigation.
Mr Trump was impeached by the House on 18 December, but a two-thirds majority vote in the Senate is required to remove him from office.
Republicans who control the chamber have made clear that the outcome is not likely.
Facing defeat, some Democrats have suggested they support other efforts to reveal “the truth”.
Chris van Hollen, a Maryland senator, said: “I don’t think the House is interested at all in opening round two of impeachment… But I do think the country deserves the truth.”
Val Demings, another House prosecutor, said Democrats would watch the Wednesday Senate vote and “make any decisions moving forward from there” about issuing a subpoena for Mr Bolton.
A spokesman for Mr Bolton declined to comment to press.
Protests are expected to take place around the country on the final day of Mr Trump’s trial.
A “Reject the Cover up Rally” is planned for Capitol Hill in the evening, as senators begin casting their votes.