The president has called climate change a hoax, and he pledged during the campaign to “cancel” the Paris deal. Few expected him to announce that the United States would remain committed to the pact.

Mr. Trump is now making clear his belief that joint global action on climate change is antagonistic to his “America first” message and could be harmful to the economy. Environmental advocates dispute the argument that the Paris accord would cost jobs.

Under the terms of the agreement, the United States cannot exit until Nov. 4, 2020 — the day after the next presidential election. That could make climate change a future campaign issue.

• Our White House reporter Michael D. Shear is tracking the latest developments in our lead story.

• Most Americans say the United States should participate in the Paris accord. But as Peter Baker writes, Mr. Trump is betting once again on his political base.