WASHINGTON — The casting call came early — the first of many unwelcome interruptions for Kamala Harris since November — consuming the Los Angeles nightclub where she was supposed to be celebrating an uncomplicated Senate victory.

With the polls closed in nearly every other corner of the country, the giant TV above the dance floor left little doubt: Donald J. Trump was almost certainly going to be president. A vacancy — standard-bearer of the Democratic Party, or at least one of them — had come open four to eight years ahead of schedule.

And people had questions.

“Literally everyone was essentially turning to her and asking,” said Juan Rodriguez, Ms. Harris’s campaign manager, recalling the scene backstage on election night. “What does this mean? What do we do?”

The sensation has perhaps grown familiar for Ms. Harris.

Less than eight months later, California’s very junior senator has emerged as the latest iteration of a bipartisan archetype: the Great Freshman Hope, a telegenic object of daydreaming projection — justified or not — for a party adrift and removed from executive power.