-- "America First" takes America out of the lead –- and places the nation virtually by itself.
Most broadly, the moment marks Trump’s decision to cede world leadership in the service of a different brand of American ideology. Trump saw it as a moment for celebration, using the White House Rose Garden to declare loyalty to American workers over world responsibilities.
"I was elected to represent the citizens of Pittsburgh, not Paris," the president said, in a tidy summation of Trumpism's promise and appeal.
With America’s exit, Germany, France and others are positioning themselves to take up mantles of world leadership, after a G7 meeting produced an odd statement on climate that was signed off on by only six nations.
But Trump is tossing aside a decade of delicate coalition-building on global warming, bucking trends that corporate America and even a growing number of Republicans have seen coming. Other world leaders said the Paris accord cannot be renegotiated, but now the international consensus on climate change in danger of breaking apart again.
Ultimately, Trump knows that his base of supporters don't trust such tables at all. The president chose to make a statement in support of a slogan that he rode to office.
The move delivers on a campaign promise, though perhaps not in the way his supporters might have thought about when they voted Trump. It will not revive coal jobs in the United States, nor will it allow Americans to drive dirtier cars or cut down on their bills if they run air conditioners colder all summer.
Then there are the ultimate stakes: the planet itself. At least while Trump is in office, it would seem that the American-driven crisis of global warming will have solutions that largely exclude America.
ABC News' MaryAlice Parks contributed to this report.