In the past several months, a meaningful debate has finally started to emerge over America’s role in the world. Politicians and analysts — left, right and center — are conceding that longstanding mistakes have brought the United States to an uncertain moment. Provoked by President Trump, they are concluding that the bipartisan consensus forged in the 1990s — in which the United States towered over the world and, at low cost, sought to remake it in America’s image — has failed and cannot be revived.

But the agreement ends there. Foreign policy hands are putting forward something like opposite diagnoses of America’s failure and opposite prescriptions for the future. One camp holds that the United States erred by coddling China and Russia, and urges a new competition against these great power rivals. The other camp, which says the United States has been too belligerent and ambitious around the world, counsels restraint, not another crusade against grand enemies.

Though still in formation, these camps are heading for a clash in the 2020 presidential race, if not in a straightforward way. Each has bipartisan backing. Each finds a little to like in Mr. Trump but rejects him as a member. And each is willing to pull back from wars in the Middle East. It’s this contest, not the sound and fury over “America First,” that is set to redefine America’s world role in the 21st century, during the rest of the Trump years and beyond.