Most presidential campaigns feature a familiar refrain: Each candidate promises to create millions of new jobs. The 2020 primaries are unusual in that nearly all the Democratic candidates, including Joe Biden, Elizabeth Warren, Bernie Sanders and Michael Bloomberg, are solemnly pledging to destroy millions of jobs by ending the shale oil and gas revolution.

The Democrats’ war on fossil fuels was on full display at the debate in Los Angeles last month, where Joe Biden, the supposed moderate, was asked if he would rein in America’s shale oil and gas production even if it meant “thousands, maybe hundreds of thousands” would lose their jobs. He unhesitatingly responded “yes,” to cheers from the audience of college students and professors. He then recited the familiar liberal riff about how investment in wind and solar power will save the economy. (Soon afterward he told a New Hampshire audience that unemployed energy workers should “learn how to program.”)

The gaffe evokes the moment in 1984 when Walter Mondale pledged during a presidential debate with President Reagan that he would raise everyone’s taxes. Mr. Mondale went on to win one state and the District of Columbia.

Curtailing U.S. oil and gas production would be economically disastrous. At least $1 trillion of U.S. economic output is related to the shale revolution, and more than 1.5 million Americans are employed in the industry. A PricewaterhouseCoopers study for the American Petroleum Institute found that at least four million American jobs are tied to the shale oil and gas revolution in areas like auto production, construction, petroleum engineering, pipe fitting, service stations, steel production and trucking.

Democrats’ quest to eliminate these jobs would hurt them in the swing states they’ll need to win to unseat President Trump. Ohio and Michigan have a combined total of more than 400,000 workers in the shale industry. Pennsylvania has another 320,000. Colorado and Florida each have more than 200,000 workers in oil and gas.