Their case was as simple as it was extraordinary, and in a bizarre constitutional twist, they were wrestling with how to present it when both the prosecutors and the jury were witnesses and victims of the offense.
How a trial might work was proving to be just as complicated.
When the Senate last met as a court of impeachment in February 2020, it was presided over by Chief Justice John G. Roberts Jr. of the Supreme Court. But the Constitution stipulates only that the chief justice must oversee the proceeding when a current president is on trial, throwing into doubt who would lead the chamber this time around.
The task could conceivably be left to the president of the Senate, which after Wednesday will be Vice President-elect Kamala Harris. Or, if Ms. Harris does not want to become embroiled in the proceeding during her first days in office, she could possibly cede the responsibility to the Senate president pro tempore, Senator Patrick J. Leahy, Democrat of Vermont.
But other constitutional scholars argued that because the charge was lodged while Mr. Trump was still president, Chief Justice Roberts should preside again.
The question was wrapped up in broader uncertainty about the Senate’s jurisdiction over Mr. Trump once he leaves office. While former government officials have been tried for impeachable offenses, no former president has. Some conservatives were pointing to the lack of precedent, and the Constitution’s silence on the matter, to argue that the Senate had no right to sit in judgment of Mr. Trump after Wednesday.
That appears to be the minority view. The Senate did try President Ulysses S. Grant’s secretary of war in the 1870s, after he had already resigned. Many legal scholars believe that is enough precedent to do so with Mr. Trump, and in any case, they argue it is highly unlikely that the Supreme Court would challenge the Senate’s decision if a majority of the body were in favor of hearing the case.
The chief justice declined to comment on Friday through a Supreme Court spokeswoman.
Senators and their aides were also trying to determine how they could alter the physical layout of the Senate chamber and attendance requirements to operate the trial safely during the pandemic. In the past, impeachment rules have required that all 100 senators sit at their desks inside the chamber whenever the trial is in session, and members of the prosecution and defense teams crammed around curved tables set up in the well of the Senate. But doing so now with an airborne virus ravaging the country — and the halls of Congress — would be unsafe.