WASHINGTON, D.C. — President Donald Trump’s defense team ended its arguments in his Senate trial Tuesday by broadly dismissing the elephant in the room: a leaked firsthand account from John Bolton, the former national security adviser, that the president directly tied aid to Ukraine to his demands for the country to investigate political rival Joe Biden.

That revelation, which emerged Sunday from a draft of Bolton’s upcoming book, has undercut the president’s defense and splintered Republicans as the trial heads into a crucial stage. On Wednesday senators are planning to start their public questioning of both the defense team and the Democratic House impeachment managers, with key votes on whether to call witnesses perhaps by the end of the week.

After initially sidestepping the Bolton reports in their arguments Monday, Trump lawyer Jay Sekulow urged the Senate on Tuesday to examine the case on the merits of the arguments and to ignore the recent reports about Bolton.

Impeachment, Sekulow said, “is not a game of leaks and unsourced manuscripts. That is politics unfortunately.” Alexander Hamilton, he continued, “put impeachment in the hands of this body, the Senate, precisely and specifically, to be above that fray.” The Senate, Sekulow said, should “end the era of impeachment for good.”

Calling witnesses would prolong the trial and introduce potentially damning testimony, upending White House and Senate Republicans’ plans for Trump’s quick acquittal.

Alan Dershowitz, a veteran defense attorney, was the only member of Trump’s 10-person team to mention Bolton’s name Monday, the first full day of the lawyers’ presentation. While Trump has argued that his July 25 call with the Ukrainian president that prompted the impeachment inquiry was “perfect,” Dershowitz at one point suggested a different defense tack, arguing essentially, so what?

“Nothing in the Bolton revelations, even if true, rise to the level of an abuse of power or an impeachable offense,” Dershowitz told the Senate in his first appearance at the trial.

Sen. John Cornyn, R-Texas, echoed that argument Tuesday, suggesting that even if Democrats could get the necessary four Republican votes for a majority in favor of subpoenaing Bolton or other witnesses, it wouldn’t make much of a difference given that the Republican-majority Senate will almost certainly vote to acquit the president.

“To me, it seems like the facts are largely undisputed; I don’t know what additional witnesses will tell us,” Cornyn said of Bolton. “We know what the facts are, and the question is whether the facts meet the constitutional standard of ‘high crimes and misdemeanors.’”

Trump’s lawyers have continued to assert that Trump had “done nothing wrong” and was genuinely interested in combating corruption in Ukraine when he directed that nearly $400 million in security assistance and a White House meeting with its president be withheld as he pushed the new government to announce probes of Biden and his son Hunter Biden. Hunter Biden served on the board of a Ukrainian energy company when his father was vice president.

The president’s lawyers have said that House Democrats didn’t provide any firsthand witnesses or direct evidence to prove their charges that Trump abused his power by pressuring Ukraine to investigate his potential rival in the 2020 presidential election and then obstructed Congress to cover it up.

Bolton, a combative conservative and a hawk on national security, declined a House invitation to testify but subsequently said he would do so at the Senate trial if subpoenaed. However, the White House issued a blanket order blocking officials and documents, calling the impeachment process illegitimate.

The Bolton allegations have fractured the largely united front that Senate Majority Leader Mitch McConnell, R-Ky., had maintained. Several mostly moderate Republicans who had been open to calling witnesses have now become more so.

Sen. Mitt Romney, R-Utah, made an impassioned speech during a party lunch Monday arguing for Bolton to be called, leading to a direct attack from colleague Sen. Kelly Loeffler, R-Ga. Afterward, Romney told reporters that “it’s increasingly likely” that there will be enough votes to subpoena Bolton.

Underscoring the chaos the Bolton report has unleashed, other once-resistant Republicans seemed to shift their position on witnesses.

Sen. Lindsey Graham, R-S.C., one of the president’s closest allies in the Senate, initially opposed calls for any witnesses, whether the Bidens or Bolton. He seemed to reverse himself Monday after the Bolton reports, and Tuesday he supported a proposal by Sen. James Lankford, R-Okla., that Bolton’s manuscript be made available for senators to read in a classified setting known as a SCIF, or Sensitive Compartmented Information Facility. The idea could be viewed as a way of getting Bolton’s information to the Senate without his public testimony.

Each senator would have “the opportunity to review the manuscript and make their own determination,” Graham tweeted.

Sen. Charles E. Schumer, D-N.Y., the Senate minority leader, rejected the proposal as “absurd.”

“It’s a book,” Schumer said of Bolton’s manuscript, which is set to publish in March. “There’s no need for it to be read in the SCIF unless you want to hide something.”