President Trump on the Truman Balcony at the White House on April 22. (Kevin Dietsch/Bloomberg)

NO DOUBT a few candidates, Democratic and maybe Republican, have yet to declare, but with former vice president Joe Biden’s announcement Thursday, the presidential field has pretty well taken shape. The lineup is diverse in talent, experience and ideology, but many prospective voters are flummoxed by what they see as the fundamental question: Who has the best chance to defeat an unqualified and toxic incumbent?

We think the best way to judge “electability” is not through polling data or race, gender or geography. Instead, let’s try to judge who would make the best president.

For us, the first requirement, in this cycle, is a fundamental commitment to the norms, habits and values of democracy. The best — and therefore most electable — challenger will be committed to civil debate and respect for opponents. She or he will embrace the nation’s diversity as an asset, rather than looking to divide with scapegoats and imagined enemies. Compromise will be accepted as a handmaiden of principle, not its opposite. Public service, and public servants, will be respected; Congress and the judiciary will be acknowledged as equal branches; law enforcement, intelligence agencies and the military will be understood to be beyond politics.

The best candidate will understand the urgency of restoring U.S. leadership throughout the world, in respectful concert with democratic allies from Mexico and Canada to Japan and South Korea to India and Europe. While Americans have been paying too little attention, authoritarianism has been on the march. Just as in the 1930s, strongmen — today in China, Russia, Iran, Saudi Arabia, Venezuela and beyond — are seeking to snuff out freedom of speech, religion, and even thought. Just as President Franklin Roosevelt warned in the days leading up to World War II, if they succeed, the world for America will become a “shabby and dangerous place.” This time, they are promoting a model of control built on modern technologies of perpetual surveillance and monitoring. And this time, so far, the United States, which should be leading the fight for liberal democracy, has been, at best, missing in action.

Of course, the United States cannot hope to succeed in that fight unless it offers the prospect of progress at home. The best candidate will have a vision of a 21st century economy that shares its fruits more equitably — but also grows dynamically enough to generate sufficient fruits for all. A proper economic plan would invest in science, education and infrastructure to generate that growth, and would show enough respect for the next generation to avoid showering free, and unpaid for, goodies on this one. Respect for the next generation demands a serious response to climate change, too.

The electable candidate will recognize the legitimate interests of diverse constituencies: the baleful effects of past and present racial and gender discrimination; the immorality of anti-gay prejudice; the needs of workers stranded by industrial evolution; the waste of forcing law-abiding immigrants into the shadows. But the electable candidate also will understand how the needs and aspirations of diverse groups overlap and intersect in a universal right to opportunity.

There’s a risk, with such a large field of candidates, that all of them will begin to lose stature. It’s important for us, the voters, to remember that a lot of able public servants have thrown their hats in the ring — and that, even from a field of nearly two dozen, none of us will find a candidate we agree with all the time or admire in every way. In return, we can ask the candidates to focus on the issues, and the case for their own capabilities, rather than on tearing each other down. That would be the surest road to electability in November 2020.