WASHINGTON — After six days of carefully choreographed oral arguments, President Trump’s impeachment trial is about to enter a volatile phase as senators are allowed to ask whatever they want of House prosecutors and White House lawyers.
It is a moment of opportunity — and peril — for both parties, as 100 senators question the House impeachment managers and Mr. Trump’s legal defense team in as many as 16 hours over two days that could shape the endgame of the trial.
Senator Josh Hawley, Republican of Missouri, wants to ask the leading House manager about the whistle-blower whose confidential complaint about Mr. Trump’s dealings with Ukraine touched off the impeachment inquiry, and about Hunter Biden, whom the president asked Ukraine’s president to investigate. Senator Angus King, independent of Maine, plans to question the defense lawyer Alan M. Dershowitz’s criteria for impeachment. Senator Kevin Cramer, Republican of North Dakota, is seeking more information about the president’s personal lawyer, who played a central role in his pressure campaign on Ukraine.
“I’m a little bit curious about Rudy Giuliani,” Mr. Cramer said.
The questions, which will begin Wednesday afternoon and could go late into the evening, will allow senators, who have been sitting restlessly in the Senate chamber for more than a week listening to dueling presentations from the two sides, the chance to participate in the proceedings, albeit indirectly. Under the arcane rules of impeachment, they are to submit written queries that will be read aloud by Chief Justice John G. Roberts Jr., who is presiding over the trial.
The result is likely to be a lively if slow-moving Senate debate. The leaders of the two parties — working in concert with the House managers and the White House lawyers — will seek to elicit damaging admissions, highlight favorable points and give their side a chance to rebut the claims made by their adversaries during nearly 30 hours of arguments since the trial opened last week.
“On the top of my mind is Professor Dershowitz’s assertion that abuse of power is not a sufficient criteria for impeachment,” said Mr. King, who has prepared more than 10 questions to be presented to both sides. He said the presentation on Monday by Mr. Trump’s lawyers “raised questions that I think the House managers need to respond to.”
When the trial resumes at 1 p.m. Wednesday, senators will submit tan-colored cards to Chief Justice Roberts that include their questions, names, signatures and the side they want the question directed to. Under the rules, senators cannot ask each other questions, but a questions can be submitted by more than one lawmaker.
The questions will alternate — one from the Republicans, then one from the Democrats and so on — for eight hours, or until there are no more. Senate leaders said they expect to get through about 10 to 12 per side before taking a break. A second session, if necessary, will take place on Thursday.
During President Bill Clinton’s impeachment trial in 1999, William H. Rehnquist, then the chief justice, opened the question-and-answer session with a lighthearted moment, telling senators that “the chair will operate on a rebuttable presumption that each question can be fully and fairly answered in five minutes or less.”
Mr. Roberts read that quote on Tuesday.
“The transcript indicates that the statement was met with, quote, laughter, end quote,” he told the senators, drawing more laughter. “Nonetheless, managers and counsels generally limited their responses accordingly. I think the late chief’s time limit was a good one and would ask both sides to abide by it.”
The leaders of both parties have strategized for days about the best questions to ask. Democrats plan to direct some to Pat A. Cipollone, the White House counsel, about what he knew about an unpublished book by John R. Bolton, the president’s former national security adviser, in which he said Mr. Trump refused to release congressionally allocated military assistance for Ukraine until the country announced investigations into his political rivals. The White House has had the manuscript for weeks. Republicans say they will ask about why the House failed to subpoena the witnesses they now say they want.
In the House, the seven Democratic managers and their staff have been preparing briefing books as they try to anticipate Republican tactics. They are preparing for personal, “gotcha” questions aimed at two of Mr. Trump’s favorite targets among the managers: Representatives Adam B. Schiff of California and Jerrold Nadler of New York.
But a person close to the House managers said they are also ready to field friendly questions from Democratic senators in the hopes they will prompt them to repeat the most damning parts of their case against Mr. Trump.
The leadership offices of both parties are coordinating the collection of questions, weeding out duplicates, rejecting off-the-wall queries and attempting to ensure that every senator gets a chance. Officials in both offices said they are helping give some order to the questions, grouping them into rough topic areas.
“Each of us, without guidance or direction, have put together our favorite topics in the form of questions,” said Senator Dick Durbin of Illinois, the No. 2 Democrat. “The sequencing and avoiding duplication is just a bookkeeping chore. The substance of the questions I presented came from me and my staff.”
During Mr. Clinton’s trial 21 years ago, which turned on his lying about a sexual affair with a White House intern, the leaders of both parties tried to screen questions to make sure the topics did not too directly address the salacious nature of the charges.
In one of the worst moments for the House Republican managers seeking Mr. Clinton’s ouster, Representative Lindsey Graham of South Carolina — now a senator participating in Mr. Trump’s trial — answered a question by saying that “reasonable people can differ” on the question of whether Mr. Clinton should be removed, giving Democrats a much-needed excuse to acquit him.
“This is the first part of the trial that has spontaneity,” said Senator Richard Blumenthal, Democrat of Connecticut, noting that the managers and White House lawyers will have to be quick on their feet. “If they try to do the canned version, it will fall flat.”
Mr. Hawley was eager on Tuesday to reveal his intended questions, sending a news release to reporters outlining the nine subjects he hoped to cover. In addition to the whistle-blower and Mr. Biden, Mr. Hawley says he will ask a series of questions about former Vice President Joseph R. Biden Jr.
Senator Christopher S. Murphy, Democrat of Connecticut, told reporters last week that it would be “good if we had some joint questions” where a Democratic and Republican senator both sign their names on a single question. One such question was submitted in 1999 — from Senator Susan Collins, Republican of Maine, and former Senator Russell D. Feingold, Democrat of Wisconsin.
It is unclear whether a bipartisan question will emerge from the current, highly polarized Senate.
Carl Hulse, Emily Cochrane and Catie Edmondson contributed reporting.