Coal miners helped win Conor Lamb a victory in a deeply red Pennsylvania district — a sign of things to come.

In 2016, West Virginia represented the epicenter of Trumpism. Trump posted a huge victory there, with 68 percent of the vote. But just 18 months later, West Virginia is emerging as a warning sign for how much trouble the Republican Party is in.

Specifically, the party may be in danger of losing chunks of white, working-class voters who propelled Trump into office. The United Mine Workers of America is set to endorse two Democrats in West Virginia.

The endorsements come just two weeks after Democrats won a special election in deeply red district in western Pennsylvania, where coal miners likely played a key role on Election Day.

On Friday, the union will “endorse Richard Ojeda for U.S. Representative in the state’s third district, as well as incumbent Senator Joe Manchin, a Democrat and former West Virginia governor,” Reuters reports.

In 2016, the union endorsed a Republican in Ojeda’s district.

Come November, Manchin’s Republican opponent could end up being Don Blankenship, the former head of Massey Energy Company. Following a huge blast at a Massey mine in 2010, which killed 29 miners, Blankenship was convicted and sentenced to prison for conspiring to violate federal mine safety standards.

Republican Party leaders are already fretting that if a convicted criminal wins the GOP nomination, the party might lose its chance to knock off a Democratic senator in a deeply red state.

In 2016, Trump aggressively embraced coal miners and often featured them at rallies and events.

The mining industry represents, “on of the purest distillations of Trump’s base, uniting right-wing business executives who hate environmental regulations and taxes along with blue-collar miners who wish America was more like it used to be when coal was king,” Politico noted.

At a White House event last year, Trump stressed, “I made them this promise, we will put our miners back to work.” But it’s not happening.

Yet so far, the job gains for coal miners are virtually non-existent, with just 130 net new jobs being created since Trump took office.

In Western Pennsylvania this month, Lamb made Democratic inroads among miners by promising to protect America’s safety net from Republicans who want to shred it. He also vowed to help coal miners protect their pensions.

“You elect this man to Congress and you won’t have to lobby him one minute,” the head of United Mine Workers of America assured voters in Pennsylvania this month. “This is a ‘yes’ vote!”

If Republicans are in danger of losing white, working-class voters like coal miners in West Virginia, they’re truly doomed come November.