With great fanfare, Trump went through the motions of carrying out a campaign promise when he negotiated a revised NAFTA. Supposedly, this would be better for the United States, and would appeal to the same blue-collar workers who deserted the Democrats to support Trump in 2016. It might even peel off some union support.

But the devil turned out to be in the details. While some the provisions of the so-called U.S.-Mexico-Canada (USMCA) deal looked good, including the one requiring Mexico to uphold its own labor standards and the rules increasing the North American content in tariff-free manufacturing, most of the deal was a stinker.

Informally, chief trade negotiator Robert Lighthizer has offered to go back to the drawing board on some aspects of the deal—if Democrats will commit to supporting a revised deal. But there are simply too many moving parts, and no such commitment has been forthcoming, and none is possible.

There are enough provisions not to like that there is a negative majority in the House against approving the deal in its present form, or in any conceivable revised version. One of the worst provisions gives big drug companies even more power to extract exorbitant prices. The major environmental groups view the deal as far worse than the status quo.

Speaker Nancy Pelosi has gone out of her way to throw cold water on the plan, partly to deny Trump bragging rights, but mostly out of objection to a lot of the content. Trump’s ace in the hole was labor support, but unions have come out in opposition, too.

Trump’s other gambit was his threat to withdraw from NAFTA if his new agreement is rejected. But on Monday, AFL-CIO President Richard Trumka trumped that ace.

“Any sovereign nation has the right to withdraw,” Trumka taunted Trump in a phone call with reporters. “I think that actually can be helpful right now.”

If Trump does act on his threat to withdraw from NAFTA, he will get little resistance from labor, and his business and farmer constituents will be apoplectic. And he would do even more severe damage to the Mexican economy, producing an even larger flow of economic refugees.

Actions have consequences. In conducting complex and delicate diplomacy, it helps to actually know what you’re doing. Trump keeps proving that he doesn’t.