In announcing on Wednesday his determination to revoke California’s longstanding authority to set its own air pollution standards, President Trump finds himself arrayed against the plain language of the Clean Air Act, California’s historical role as a laboratory for tough new environmental rules and the express wishes of several major automakers and two-thirds of the American people .

It is, further, one more intended nail in the coffin of President Barack Obama’s strategy to reduce greenhouse gases and, coming as it does on the eve of a big United Nations conference on global warming, a thumb in the eye to the rest of the world.

A monumental legal battle lies ahead. California’s authority to set its own pollution standards dates back to the 1960s, when the state passed laws to deal with its crippling smog problem. The federal Clean Air Act of 1970 codified that special authority, as long as the state could show a compelling need for standards stricter than the federal government’s. Congress has repeatedly reaffirmed that right, and in 1977 it said other states could legally opt in to California’s standards. Thirteen have now done so.

Over time, strategies adopted in California to control smog-producing pollutants became standard across the country. So, too, with carbon dioxide, the main greenhouse gas. California’s decision in 2002 to add greenhouse gases to the list of pollutants it wanted to control — a decision approved by the Obama administration seven years later — arguably accelerated the push for zero-emission and low-emission vehicles like plug-in hybrids. (Tailpipe emissions are now the nation’s single biggest source of greenhouse gas emissions.)