Tellingly, the Republicans on the Senate Intelligence Committee paid no heed to the talking points distributed in advance by the Republican National Committee at the behest of the White House. Instead of attacking Mr. Comey’s credibility, as the R.N.C. and Donald Trump Jr. did, the Republican senators praised him as a patriot and dedicated public servant. They largely accepted his version of events, while trying to elicit testimony that would cast Mr. Trump’s actions in the most innocent light possible.

Mr. Comey cooperated to some extent by trying not to go too far beyond the facts as he presented them, declining, for instance, to say whether he thought Mr. Trump’s statements amounted to obstruction of justice.

“In a credibility battle between Trump and Comey, everybody knows Comey is going to win that war,” said Adam W. Goldberg, who was an associate special White House counsel under Mr. Clinton during Kenneth W. Starr’s investigation.