WASHINGTON — As 48,000 GM employees hit the picket line on Monday, President Trump bragged that American auto workers “have been been very good from the standpoint of voting.”

But this strike—and everything that led to it—may test that.

Trump ran hard on promises to save the industrial Midwest and revitalize American manufacturing. His narrow White House win came after surprising victories in Wisconsin, Michigan and Pennsylvania, where just enough traditionally Democratic, blue-collar voters switched parties or stayed home.

Almost three years later, the economy has continued to grow. But its benefits are being felt unevenly, and many workers are still feeling the squeeze in places like Warren, Michigan, one of the places where GM recently “idled” a factory. Sunday night’s decision by GM’s United Auto Workers to strike, as they try to win contract concessions and get GM to reopen those plants, puts a spotlight on whether Trump has delivered for the workers who helped put him in office.

It’s the largest worker strike in the U.S. in a decade. If it drags on, it could become problematic for Trump, who needs to show workers he’s on their side to win re-election.

“I think it will hurt him,” said Daniel Ujczo, an international trade lawyer and auto industry expert in Ohio. “The president is in a very difficult position right now. Democrats are sitting there waiting tooth and claw for him to prove that he really isn't on the side of labor, with the hopes that they could gain those votes back in critical states.”

Trump casually tweeted “here we go again” when the strike began, calling on both sides to “make a deal” on Sunday. On Monday, he offered federal mediation to the two sides, “if that’s what they want.”

“Hopefully they'll be able to work out the GM strike quickly,” he said at the White House Monday evening. “We don’t want General Motors building plants outside of this country,”

Trump met with GM CEO Mary Barra a couple of weeks ago, and he has occasionally spoken out about the GM-UAW negotiations. That includes a frustrated attack on GM’s leaders for closing a plant in Lordstown, Ohio, earlier this year, and an attack on David Green, a local UAW leader who’s said Trump hasn’t done enough for them.

Green was the union rep in Lordstown when the plant shut down. Like a lot of his colleagues there, he recently took a transfer, to a plant in Indiana. He declined to talk about the political ramifications of the strike. But he made clear how hard it’s been for him and his fellow workers, who first faced relocation and now are on strike, with only a $250 weekly stipend from the union to sustain them. “It’s tough right now,” he said.

How Trump responds matters to those workers. But they’re also watching how his potential Democratic opponents respond.

Former Vice President Joe Biden was part of the Obama administration when it helped save GM during the auto bailout. He tweeted that he was “proud to stand” with the UAW workers “to demand fair wages and benefits for their members.” Sen. Elizabeth Warren (D-Mass.) said the UAW workers “deserve good wages, comprehensive benefits, and economic security.”

Sen. Bernie Sanders (I-Vt.) was even more vocal, pointing out that GM got a $50 billion bailout in 2008.

"I am proud to support the UAW workers who are standing up to the greed of General Motors,” he said in a statement Sunday. “Today, our message to General Motors is a simple one: End the greed, sit down with the UAW, and work out an agreement that treats your workers with the respect and the dignity they deserve."

GM made roughly $8 billion in post-tax profits in 2018. Some of that went to its employees as part of a profit-sharing agreement that’s part of the union contract. But the auto manufacturer infuriated the union and alarmed workers when it decided to shutter four major plants, including two in swing-state Michigan and another in Ohio, part of its pivot away from smaller cars. Many of those plant workers were forced to uproot their lives or commute long distances to keep their jobs.

It’s likely the strike will be front of mind as Biden, Sanders and other Democratic candidates address an AFL-CIO summit in Philadelphia on Tuesday.

Neither the union nor GM wanted to weigh in on the political implications of their stalemate.

“Our goal remains to reach an agreement that builds a stronger future for our employees and our business,” GM spokesman David Barnas told VICE News.

UAW workers made some significant concessions in 2008 to help keep the company afloat, and they argue GM should now return the favor.

“The impact will be larger and worse the longer this strike goes on.”

“Our focus is on our members and getting our contract. 2020 is a lifetime away,” UAW spokesman Brian Rothenberg told VICE News. “We stood up for this company when they needed us. And now we need this company, now that it's very profitable, to stand up for us. We’re not going to engage in politics. This is about our members: their livelihoods, their futures, and their pocketbooks.”

The strike could threaten one of Trump's only remaining chances to pass meaningful legislation this term. He's still waiting on Congress to ratify his renegotiated North American Free Trade Agreement, known as the U.S.-Mexico-Canada Agreement, or USMCA. But unions are skeptical of the deal and are pressuring Democrats to make sure that its labor standards—which regulate how workers in Mexico are paid and treated—are enforceable.

“I can’t envision a scenario where [House Speaker Nancy] Pelosi brings USMCA to a vote while UAW is on strike,” Ujczo said. "The optics of that are horrible."

If this strike ends quickly, this probably becomes just a blip in the national news and not much concern for the president. But the longer it drags on, the more it may mean for Trump.

“The impact will be larger and worse the longer this strike goes on,” former Michigan AFL-CIO President Mark Gaffney told VICE News.