Senator Harry Reid says Democrats should move to curtail the filibuster if they win the White House and Senate in November only to run up against persistent use of the tactic by Republicans.

“Unless after this election there is a dramatic change to go back to the way it used to be, the Senate will have to evolve as it has in the past,” Mr. Reid told me, referring to a former tradition of rarely mounting filibusters. “But it will evolve with a majority vote determining stuff. It is going to happen.”

He has condemned Republican reliance on the filibuster to impede President Obama. Mr. Reid’s frustration ultimately led Senate Democrats in 2013 to weaken the minority party’s ability to block most executive branch nominations. But he won’t be in office to challenge the filibuster. He is retiring.

However, he is the first to publicly express what other lawmakers and aides have talked about more quietly — the possibility that Democrats would take drastic action if they were triumphant at the polls only to be blocked by the gridlock that has plagued Washington in a new Clinton administration.