Democrats have long been able to rely on the support of labor unions and their members. President Trump won in 2016 by eating away at that advantage in key states. Hillary Clinton still took home more union votes overall, but Trump narrowed the gap to a mere nine percentage points — versus an 18 percentage point advantage for Barack Obama in 2012, and 30 percentage points for Bill Clinton in 1992.

Union workers, many of them disillusioned by globalism and the apparent indifference of American political elites, really bought in to Trump's "Make America Great Again" promises. In March of last year, Trump enjoyed a whopping 62 percent approval rating among union members.

Unfortunately, the president has repaid that endorsement with bupkus.

Over the weekend, Fox News' Chris Wallace asked Richard Trumka, president of the AFL-CIO (the country's largest labor federation), how he'd score Trump's efforts so far on behalf of working people. "Unfortunately, to date, the things that he's done to hurt workers outpace what he's done to help workers," Trumka said, listing a whole string of topics — from infrastructure to taxes to regulations to trade — on which the president has either failed to deliver or actively made things worse.

Trump fired back on Labor Day, tweeting, "Richard Trumka, the head of the AFL-CIO, represented his union poorly on television this weekend. Some of the things he said were so against the working men and women of our country, and the success of the U.S. itself, that it is easy to see why unions are doing so poorly." Of course, Trump's response failed to address a single one of the substantive points Trumka brought up.

This is likely because there isn't much Trump could say to counter Trumka's charges.

Let's take the president's recent tax cut package. The direct benefits of the tax cuts overwhelmingly favored the wealthy and businesses. But Trump and the Republicans sold this design on the premise that companies would invest more in job creation and wage hikes. This argument was absurd on its face when it was made, and it's proven a total bust since.

As Trumka noted, wages for most American workers are stagnant. (In fact, Americans have actually lost ground recently once you factor in price increases.) A whole host of changes — from unions' decline to fiscal and monetary policy changes to trade to antitrust enforcement — have created an economy which, even when it's growing handily, siphons off most of the newly created wealth to the rich.

These changes were justified with the ideology of "trickle down economics" — an ideology that Trump, for all his supposed concern for working people, effectively endorsed by signing the tax cut. And by further lowering the barriers to shareholder payouts, Trump has likely made the extraction worse, even as the economy grows.

Or consider Trump's aggressive deregulation. After coming into office, Trump worked hand in hand with congressional Republicans to make it easier for federal contractors to underpay workers and shove them into unsafe conditions. They've placed blatantly pro-corporate appointees in charge of the regulators that enforce worker safety, and undercut the ability of the Occupational Safety and Health Administration and other agencies to police those violations. They scuttled an Obama-era rule that would've significantly increased the number of workers who benefit from overtime pay.

Both of Trump's appointments to the Supreme Court — first Neil Gorsuch, and now Brett Kavanaugh — have a history of siding with businesses over workers and labor. The recent Janus decision, in which Gorsuch supplied a key vote, kneecapped public sector unions' ability to bargain for their members or amass resources.

Trump's record on trade is more complex. As Trumka noted, many of the changes Trump has pushed in NAFTA negotiations would be positive for workers. But Trump's breezy confidence that he can score a deal with Mexico and ignore Canada isn't workable, either economically or politically. Congress holds all the cards here, and would never go for a NAFTA deal that went forward without Canadian sign-on. On this subject, whatever pro-worker instincts Trump may have are overwhelmed by his raw incompetence.

Now, whether union members will actually abandon Trump in this year's midterms and the 2020 presidential election is another matter.

Trumka himself made no bones about where he stands: "Unfortunately, Democrats support working people more than Republicans have." Randi Weingarten, the head of the American Federation of Teachers, is also encouraging unions to line up against Trump. And overall, union members still support Democrats on a generic ballot, 47 percent to 34 percent.

But the economy is doing well, and most union members are not in leadership positions with close ties to the Democratic Party. Trump's support among union voters has dropped precipitously since its 62 percent high. But that initial peak was pretty tremendous. Even Trump's 47 percent approval in March of this year (unfortunately the latest data available) is an impressive haul by GOP standards. It remains unclear just how much damage Trump can do to union members' trust in him.

That said, the president seems determined to find out.