Democrats are already raising alarms that the inquiry initially hailed as a bipartisan breakthrough will be too constrained to be legitimate. But the one-week limit put on it by Mr. Flake meant from the start that the F.B.I. would be hard-pressed to do a full investigation into all the accusations surrounding Judge Kavanaugh. In addition, Mr. Flake and his allies seemed mainly interested in having the named attendees at a gathering at the center of the Kavanaugh questions be interviewed by experienced federal investigators before voting on the nomination.

Still, it wasn’t what most Senate Republicans wanted. They were more than ready to use their majority to muscle Judge Kavanaugh on to the Supreme Court no matter what Democrats desired. Senate Republicans have been fuming at Democrats for their handling of a letter from Christine Blasey Ford saying she was assaulted by Judge Kavanaugh when both were in high school. With confirmation in sight, they were in no mood to brook more calls from Democrats for further delays and investigations.

But after Mr. Flake’s announcement on Friday that he, Ms. Collins and Senator Lisa Murkowski, Republican of Alaska, wanted the F.B.I. to take a new look into reports of misconduct by Judge Kavanaugh before a final confirmation vote, President Trump and Senator Mitch McConnell, the Kentucky Republican and majority leader, had no choice. Without those Republican votes, Judge Kavanaugh’s nomination was probably dead.

Mr. McConnell was clearly unhappy with the sudden turn of events. At a meeting in his Capitol office, he warned Mr. Flake, Ms. Collins and others that another week would only allow time for opponents to churn up more trouble for Judge Kavanaugh while prolonging an ordeal for the nominee and his family. Not to mention that no Senate leader likes to lose control over the agenda to a rump group of members who exert their individual leverage like Mr. Flake and his allies did. It was reminiscent of 2005, when the bipartisan Gang of 14 came together to defuse a showdown over judicial filibusters, undermining Bill Frist, a Tennessee Republican who was then the majority leader.