MIAMI — A sense of doom spread not long ago among weary Florida Democrats, and not over a viral pandemic.

They had lost winnable races for governor and Senate two years ago in nail-biter recounts. Many now feared that the state’s voters, with their reflexive disdain for political revolution, would spurn Bernie Sanders in November, giving President Trump a far easier path to re-election.

Florida’s long status as a swing state could be over.

Then came Joseph R. Biden Jr.’s resurgence. Democratic leaders, who expect Mr. Biden to trounce Mr. Sanders in Tuesday’s primary, began breathing more easily. But come November, clawing back votes in the nation’s biggest battleground state will still be a daunting task.

For all of the state’s foibles, from Florida Man to hanging chads, Florida remains a microcosm of the country, a mirror reflecting the contradictions and divisions of the national electorate. It is a primary state that offers a glimpse of the general election, in terms of which candidates win and, perhaps more important, which voters show up.