WASHINGTON — Hillary Clinton faces a strategic choice. She can concentrate on closing off Donald Trump’s potential openings with the white working class. Or she can build large leads among more affluent voters, many of whom are moderate and see Trump as dangerous, extreme and temperamentally unfit.

She will necessarily do some of both — she needs a decent share of the blue-collar vote to hold key Midwestern states — and she will have to rally what have been core Democratic constituencies: younger voters, who eluded her during the primaries, African-Americans and Latinos. But the direction of her campaign and her selection of a running mate will depend in significant part on the class tilt of her strategy.

For the moment, however, her decisions are easy compared with those confronting Republicans. Trump’s stubborn refusal to transition away from his persona during the primaries has put the party’s leaders in an impossible position.

They can try to prop up their presumptive nominee in an effort to avert a quick collapse that could endanger their entire party in November. Or they can distance themselves from him now in the hope of disentangling their ticket from what is beginning to look like an epic disaster.

But this is a classic Catch-22: The very process of pulling back from Trump further weakens him, making the calamity the party fears even more likely. And Democratic pollster Stan Greenberg says Republican candidates for the House and Senate would risk large defections from their base if they are seen as sabotaging Trump.

This is why House Speaker Paul Ryan ended up in the anomalous position of reiterating his support for Trump even as he was condemning the racism of his candidate’s attacks on Judge Gonzalo Curiel. Endorsing Trump means always having to say you’re sorry.

Clinton set up what was by far the best period of her campaign with a sweeping assault on Trump to which he offered only a feeble reply — while drawing little defense from his own party. Clinton’s primary victories last week opened the way for endorsements from Obama and Elizabeth Warren even as Bernie Sanders signaled he understood that his campaign was nearing its end.

Yet Sanders’ comments after a White House meeting with Obama pointed to the choice Clinton confronts.

Sanders promised to “work as hard as I can to make sure that Donald Trump does not become president of the United States.” But he also pledged to continue “to oppose the drift which currently exists toward an oligarchic form of society where a handful of billionaires exercise enormous power over our political, economic and media life.” Sanders’ enthusiasm for the first objective will depend in part on Clinton’s enthusiasm for the second.

Still, there’s a lot to be said for the upscale strategy. Clinton’s forceful emphasis on Trump’s character and Vice President Joe Biden’s talk of his “authoritarianism” will resonate in better-off suburbs and urban precincts.

“I do think his temperament and divisiveness are going to discredit him with voters who might otherwise have been available to a Republican nominee among the white college educated,” said David Axelrod, formerly Obama’s senior adviser. And given a Democratic leaning in the electorate reflected in Obama’s 5 million vote margin from 2012, Trump is unlikely to gain enough in the white working class to offset his losses among the well-to-do. “He can’t trade votes and win,” Axelrod said.

Moreover, Greenberg sees a focus on Trump’s personal volatility as having helpful ricochet effects with other constituencies. To the extent that Trump is forced by the party to tone down his rhetoric (just watch his flat, Teleprompter-driven address from last Tuesday), he may start losing some of his magic with working-class voters.

And Greenberg argues that Clinton knows she has to offer a strong economic message with a populist feel to win over the millennial voters who flocked to Sanders. Appeals aimed their way will simultaneously help earn Sanders’ blessing and pick up the white working-class votes she’ll need.

The fact that the strategic playing field now favors Clinton points to how urgent it is for Trump to turn the campaign narrative to her weaknesses, which he says he’ll do this week.

His challenge is that while most of the negative information about Clinton is already well-known, each day seems to bring new revelations about Trump’s past business practices and personal habits. And out-of-control attacks on Clinton will only provoke more questions about Trump’s temperament.

For the first time all year, being Hillary Clinton is easier than being Donald Trump.

E.J. Dionne is a columnist for The Washington Post. His email address is: ejdionne@washpost.com. Twitter: @EJDionne.