“Emotions are running really high now at this stage of the most bizarre presidential election of my lifetime,” she said. “After the election, I believe there will be a reassessment of how we should approach judicial nominees.”

Ms. Collins, who was part of the so-called Gang of 14 that in 2005 struck a deal that judges should not be blocked except under extraordinary circumstances, said the Senate should return to that standard.

“I certainly understand that the court has become much more ideological than is desirable for that institution, and that is why there are those who have taken what I believe to be an untenable view,” she said. “We don’t even know who her Supreme Court nominees are going to be, so how could we possibly draw a line in the sand? I certainly hope we don’t go down that route.”

Other senators with influence on judicial matters have sought to stave off the idea of a running blockade. Senator Lindsey Graham, a South Carolina Republican who sits on the Judiciary Committee, joined in resisting hearings for Judge Garland, but he told me months ago that he had already warned his colleagues that he would be ready to back a nominee by Mrs. Clinton as long as the choice was qualified.

And Senator Charles E. Grassley of Iowa, the Judiciary Committee chairman who has been pummeled by Democrats for refusing to set hearings on Judge Garland, indicated recently that he intended to act on the new president’s Supreme Court nomination. “If that new president happens to be Hillary, we can’t just simply stonewall,” he told a group of radio reporters.

If Democrats win the Senate and Mrs. Clinton becomes president, Republicans could try to block a nomination through a filibuster. But both parties fully expect that Democrats would quickly take procedural steps to deny Republicans the ability to do so, just as they did in 2013 when they lowered the threshold for breaking filibusters against most judicial nominees from 60 votes to a simple majority.

The Supreme Court was not included in that change because some senior Democrats feared the decision might backfire if it left them unable to block a future conservative choice they opposed. But after the Republican treatment of Judge Garland, Democrats would have little reluctance to force through the change now if Republicans carried out a Supreme Court filibuster.

Of course, this all becomes moot if Donald J. Trump is elected president and Republicans hold the Senate. Then it will be Democrats searching for ways to hold up Mr. Trump’s court choices.