On the second day of the trial, Democrats worked methodically to dismantle Trump's long-standing allegation that Democratic presidential contender Joe Biden acted improperly toward Ukraine while vice president.
But senators showed increasing signs of restlessness, with many wandering to the rear of the chamber where they could make phone calls and check their smartphones.
"It does seem that after about an hour and a half, they start repeating themselves as if you could impeach by just kind of repeating the same thing by repetition. We are ready for the president's team to put their defense on. The president didn't have a chance to do that in the House," said John Barrasso, Republican senator from Wyoming.
Democratic senator Mazie Hirono countered, saying, "Well, you know what? They spent all of Tuesday fighting back all of our efforts to present new evidence and new documents."
And signs emerged that the Democratic case was losing some of the public's attention, as well. Throughout the session, there were empty seats in the gallery overlooking the Senate floor.
Television ratings were down. About 8.9 million viewers watched the first day of arguments on Wednesday, falling short of the roughly 11 million who watched on Tuesday, according to Nielsen ratings data.