Trump withdrew the United States from participation in the Paris accord to combat climate change, and he falsely asserted that the United States had the world’s “cleanest air” and “cleanest climate” and even the “cleanest water.”

The United States actually ranks 27th in the world, according to the authoritative Environmental Performance Index, a project of Yale and Columbia universities. It ranks 10th for air quality — but 88th on exposure to particulate matter, an indication of the health effects from pollution — and 29th for water and sanitation. The United States is tied for first place — with nine other countries — for the quality of drinking water.

As for whether things have improved under Trump, that’s hard to track in the available data — in fact, the number of unhealthy days in the United States went up from 2016 to 2017, according to government data — but he has taken a number of actions that could reverse or slow the gains made in air and water quality since 1990.