Last year, Democratic interest groups and voters berated Senator Chuck Schumer of New York, the minority leader, for backing off a spending fight with President Trump rather than forcing a government shutdown early in his term.

Activists called for Mr. Schumer’s ouster. Some Democratic lawmakers seethed. Protesters jeered outside his Brooklyn home. The outcry reached such a pitch that he postponed public appearances to promote a new book he had written and hunkered down amid questions about whether he could continue as the Democratic leader.

Twenty months later and in the wake of a sweeping electoral victory he engineered and funded, Mr. Schumer’s aides say he has locked down another term in that post, having secured commitments of support from enough Democratic senators to be elected majority leader in a private vote scheduled for next month.