Trump's Twitter tantrums are now imperiling the entire U.S. auto industry.

Trump took to Twitter Saturday to threaten a trade war with the European Union after his proposal to hike tariffs on steel and aluminum was blasted by lawmakers on both sides of the aisle and in multiple countries, as well as trade groups, economists, and major U.S. employers.

Besides embarrassing the nation, Trump’s infantile Twitter tantrum threatens to sink the auto industry after President Barack Obama saved it from collapsing.

Trump announced his proposal to impose massive new tariffs on imported steel and aluminum on Thursday. The announcement was followed by an immediate drop in the stock market, and sharp rejection from other world leaders.

Jean-Claude Juncker, president of the European Commission, said that the E.U. would respond to Trump’s proposed hike by imposing tariffs on American products including Harley-Davidson motorcycles, Kentucky bourbon whiskey, and jeans.

On Saturday, Trump responded with a tweet.

“If the E.U. wants to further increase their already massive tariffs and barriers on U.S. companies doing business there, we will simply apply a Tax on their Cars which freely pour into the U.S.,” he wrote. “They make it impossible for our cars (and more) to sell there. Big trade imbalance!”

If Trump follows through with the threat, he will imperil the future of the U.S. auto industry, which President Obama pulled back from the brink of collapse.

Trade groups like the American Automotive Policy Council — which represents FCA US, Ford Motor Company, and General Motors Company — tried to warn Trump of the consequences of hiking tariffs on steel and aluminum. In a statement released last week, the group said the move “would place the U.S. automotive industry, which supports more than 7 million American jobs, at a competitive disadvantage.”

Despite knowing that he would imperil jobs and entire industries, Trump is still barreling ahead with his reckless proposal.

“These proposed tariffs on steel and aluminum imports couldn’t come at a worse time,” Cody Lusk, president of the American International Automobile Dealers Association, told Bloomberg. “Auto sales have flattened in recent months, and manufacturers are not prepared to absorb a sharp increase in the cost to build cars and trucks in America.”

It’s always been clear that Trump is threatened by President Obama’s legacy and wants nothing more than to undo it — but now, it appears that Trump is willing to endanger the entire U.S. economy to do it.