“When you make an argument like that, you better be sure that your entire audience is with you,” said James G. McGovern, a criminal defense lawyer at Hogan Lovells in New York and a former prosecutor.
Multiple Republicans said afterward that they had not at all been moved by Mr. Schiff. “It seems to me their case is weaker today than it was yesterday,” said Senator John Barrasso of Wyoming, the No. 3 Senate Republican, as he faulted Mr. Schiff.
But Anne Milgram, a former attorney general of New Jersey and now a law professor at New York University, described Mr. Schiff’s sharp criticism of Mr. Trump as a “wise calculation,” because unlike a regular jury trial, Mr. Schiff does not need a unanimous verdict. The argument was aimed, she said, at the four or so moderate Republicans whose votes Democrats will need to call witnesses at the trial.
Regardless of the risk, it was clear on both sides of the aisle — and to experienced prosecutors who watched — that after a long day of complicated and sometimes monotonous testimony, Mr. Schiff’s oratory broke through. Mr. Schiff apparently thought so himself. He posted the last eight minutes, the most dramatic part of his speech, on Twitter Thursday night, and by Friday evening it had been viewed more than 5.9 million times.
“Sometimes when Schiff steps to the mic I think he’s a little scripted,” Ms. Milgram said. “I did not feel that last night. I thought it was the most authentic I have seen him. He sort of crossed into another level.”
Mr. Schiff opened by carefully leading the Senate through the House’s case that the president abused his office by trying to enlist Ukraine to investigate his political rivals, weaving in bits and pieces of testimony and commentary along the way. He then turned to his Senate audience and stated what he believes to be the obvious: Mr. Trump is guilty.
“Do we really have any doubt about the facts here?” Mr. Schiff asked. “Does anybody really question whether the president is capable of what he’s charged with? No one is really making the argument Donald Trump would never do such a thing, because of course we know that he would, and of course we know that he did.”