“Republicans may run but they can’t hide,” said Senator Chuck Schumer of New York, the Democratic leader. “There will be votes at the beginning on whether to call the four witnesses we’ve proposed and subpoena the documents we’ve identified. America and the eyes of history will be watching what my Republican colleagues do.”

At the moment, Republicans appear content to plunge ahead with their approach modeled on the Clinton proceeding, and Senator Mitch McConnell, Republican of Kentucky and the majority leader, is confident he has his troops on board.

As in the Kavanaugh confirmation, Mr. McConnell has no worries whatsoever about the vast majority of Senate Republicans who appear ready to acquit the president without going much beyond opening arguments. On Twitter and in interviews, they argued that it was not the Senate’s responsibility to repair what they saw as a defective investigation by the House.

“Our job is to vote on what the House passed, not to conduct an open ended inquiry,” Senator Marco Rubio, Republican of Florida, declared on Twitter.

Instead, Mr. McConnell’s concern in the Kavanaugh fight was the handful of Republicans who might break from the pack — Ms. Collins, Lisa Murkowski of Alaska, Jeff Flake of Arizona — and sink the nomination.

As a result, Mr. McConnell needed to pay heed to their wishes as they pushed for reconvening the hearings to allow Ms. Blasey Ford to testify, and later to reopen the background check of Judge Kavanaugh to pursue new material that surfaced about his conduct. The renewed F.B.I. investigation was very limited in its scope, frustrating Democrats, and produced no damning material.