Fifty years ago, millions of people took to the streets to protest the air and water pollution that were making us sick. Today, millions are sheltering inside to try to stem the spread of a very different kind of sickness, Covid-19.

Out of that first Earth Day eventually came — under a Republican administration — the Clean Air Act of 1970 and the Environmental Protection Agency. That agency was given one mission: to protect human health and the environment. From time to time, Republicans and Democrats have worked together to strengthen the authority of the Clean Air Act. Further, the Supreme Court in 2007 affirmed that the E.P.A. has the authority to regulate the emission of greenhouse gases that warm our planet.

Over the decades, people began to “celebrate” Earth Day. It became a feel-good commemoration. We were seeing the heartening results of stronger antipollution regulations. We began to take for granted that we had a right to clean air.

That has turned out to be a disastrous mistake under the Trump administration.

To run the E.P.A., the president chose a former lobbyist for the coal industry, Andrew Wheeler, who has spent his time there eviscerating the steady progress made to keep America’s air clean.