It was just what Marco Rubio and Bernie Sanders had promised their supporters all along.

Rubio was routed in early races, but didn’t get discouraged. He pressed ahead with his message and connected with voters—and they responded by delivering a stunning, decisive margin affirming his potential.

That’s what happened on Sunday in Puerto Rico, where Rubio collected more than 70 percent of the vote—far more than he needed to sweep the island’s 23 delegates. Donald Trump was an afterthought, at 13 percent; Ted Cruz a distant third; and John Kasich a rounding error.

In the morning, though, the Republican race will return to the mainland, and to the grim reality confronting the Florida senator: Even with his latest win, he has no clear path to securing a majority of the delegates, and unless he can rally to win his own state, he may soon be forced from the race.

Bernie Sanders staged the political revolution he frequently invokes. He won the Maine caucuses decisively, defeating Hillary Clinton 64 to 36 percent, despite her institutional support. In Portland, so many voters came out to make their voices heard that the line stretched for more than a mile.

Sanders’s victory, like those the day before in Kansas and Nebraska, affirms his ability to prevail in contests that favor organization and grassroots support, and in states with predominately white electorates. He needs to continue to pile up wins in states like Maine. But they won’t be enough. Unless he can expand his reach beyond them, he, too, lacks a path to the nomination.

On Sunday night, Sanders faced that grim reality, as he debated Clinton in Flint, Michigan. Voters there will go to the polls on Tuesday—and the state is precisely the sort of contest that Sanders must begin to win if he wants to prevail at the convention.

—Yoni Appelbaum