This week’s NATO summit in Washington was supposed to be a celebration.

Seventy-five years after its founding, the alliance is bigger and more relevant than it’s been in decades. Transatlantic ties are strong again. Spurred by Russia’s invasion of Ukraine, allies are united — thanks, in no small part, to U.S. leadership.But as the city prepares to play host to dozens of heads of state and government, few are in the mood for a party. The U.S. president who championed NATO’s revival is in serious trouble. On both sides of the Atlantic, far-right, isolationist politics loom.

NATO, at 75, is still vigorous. Yet it’s hard not to wonder how the alliance will look a year from now — whether it will make it to 76 alive and well.

Over three days of meetings starting Tuesday, President Biden and Western leaders will make the case that NATO and the post-World War II order have good years ahead.Allies will recall the history that brought them together and rally around the need to counter a revanchist Russia. They will outline how they are working to help Ukraine. And they will signal that NATO has a close eye on the budding military partnership between Beijing and Moscow.Outside the halls of the Walter E. Washington Convention Center — where the formal business of summitry will take place — the storyline will be less sanguine, with a focus on Biden’s fitness for office, the possibility of a second Trump presidency and political chaos in France.

The messaging from the summit will be calibrated to make a case for the alliance, to try to ensure it weathers the political storm intact. Allies will stress significant increases in defense spending and offer Ukraine more military aid — though the package is less than some NATO officials hoped and will not come with much progress on membership.