With Trump's legal team resting its defense of the president, the impeachment trial now moves to its next phase: asking written questions.
Over 16 hours, senators of both parties will submit questions to House managers prosecuting the case and Trump's defense lawyers, with Chief Justice John Roberts, who is presiding over the trial, reading the questions aloud on the floor of the chamber.
During the impeachment trial of Bill Clinton in 1999, senators asked more than 150 questions across two days.
Republicans and Democrats reached a deal in which the parties will alternate turns asking questions for up to eight hours on Wednesday. The same rules and duration of question time has been allotted for Thursday.
That sets the stage for a Friday vote on witnesses.
According to Democrats, multiple possible witnesses have first-hand accounts of what they say as a quid-pro-quo scheme with Ukraine that forms the basis of the two impeachment charges Trump is facing.
Democrats say bringing witnesses into the impeachment trial is essential to conducting a fair trial, while conservatives fear the entry of witnesses can inject uncertainty into the proceeding and prolong the process.
Among the sought-after witnesses is former National Security Adviser John Bolton, who captured Washington's attention following the release of revelations in his forthcoming book that Trump allegedly told Bolton that the military assistance was only to be released after Ukraine opened investigations into his Democratic rivals. Those purported book details, first reported by The New York Times, placed pressure on senators to vote to allow witnesses into the trial.
Trump's defense team, in response, argued that a manuscript of Bolton's book would be "inadmissible" in the trial. Defense lawyer Jay Sekulow saying impeachment "is not a game of leaks and unsourced manuscripts." And anything Bolton would have to offer in person about his conversations with Trump, argued Trump attorney Alan Dershowitz, would not rise to the level of an impeachable offense.
Whether Republicans can defeat the Democrats' push for witnesses, including Bolton, remains an open question.
Senate Majority Leader Mitch McConnell told Republicans in a closed-door meeting late Tuesday that the party does not yet have the votes to block new witnesses, but that does not mean Democrats will be able to subpoena Bolton, or any other witness. That decision will come down to moderate Republicans including Mitt Romney, R-Utah, Lamar Alexander, R-Tenn., Lisa Murkowski, R-Alaska and Susan Collins, R-Maine who have indicated they may be open to hearing from witnesses, but their final decision is still unknown.
Trump's defense team argued earlier this week that the case against the president presented by Democrats does not constitute any impeachable offenses.
Lawyers for Trump have also accused Democrats of trying to invalidate the result of the 2016 election. They also argued that Trump has not committed any crime and therefore cannot be removed from office, even though many legal scholars say breaking a law is not required in order to secure an impeachment conviction that would remove a president from office.
Democrats have impeached Trump for abuse of power and obstruction of Congress for what the prosecution team says was a campaign to pressure Ukraine into opening investigations into Trump's political rivals and held-up $391 million in congressionally approved security assistance in order to apply leverage on Ukrainian authorities. House Democrats say the White House's refusal to cooperate with the impeachment investigation is proof of a cover-up and amounts to obstruction.