WAYNESBURG, Pa. — In less than five months, the true test of President Trump’s staying power in the Rust Belt will finally be here. A House seat in southwestern Pennsylvania, which voted solidly for Trump in 2016, is up for grabs in a special election on March 13.

Republican Tim Murphy held this seat for 10 years until it was revealed that the politician, who is married and pro-life, asked his mistress to consider an abortion in the midst of a pregnancy scare. The news prompted a national scandal and his ouster this fall.

Now, the first post-Trump election in Appalachia is approaching, and the result could signal how the crucial 2018 midterms will be decided next year. While the special election in Alabama for a senate seat on Dec. 12 is getting all the press, this one could be the real game-changer. Especially because the Democrats have a really good shot at taking the seat with their candidate Conor Lamb.

Lamb, a former assistant US attorney and Marine veteran, fits his socially conservative 18th District like a glove. Young, fresh and charming, the 33-year old comes from a politically active family and is focused on two major issues for his constituents: the economy and the opioid crisis.

On social issues he is more in tune with his voters than with his party’s national left-wing platform.

“I am pro-Second Amendment,” he said in an interview after securing the nomination, adding a caveat that “we need to have the conversation” about gun regulation.

On abortion, despite his Catholic faith, he said that “choice is the law of the land,” which he will uphold.

But, asked whether he would support Nancy Pelosi for speaker of the House if Democrats win back the majority, he didn’t offer his support. Instead, he said that answering would be “presumptuous.”

The 18th District is overwhelmingly white and economically mixed — including wealthy college-educated professionals, lower-educated poor and a lot of middle-class blue-collar Democrats in between. Although a historically Democratic district (there are nearly 70,000 more registered Democrats than Republicans here), Trump won it by about 20 points.

Still, there is “the potential to elect a Democrat” in the district, said Mike Doyle, a Democratic congressman in Pennsylvania, “but it has to be the right kind of Democrat.”

“That’s why we’re kind of excited about Conor, because he sort of fits that bill,” Doyle added. “Military background, prosecutor, Second Amendment believer. A lot of his positions . . . are in sync with a lot of positions that Democratic voters have in . . . that district.”

Former Congressman Jason Altmire, a pro-life, pro-gun Democrat, agrees the seat is winnable as long as the candidate’s message is authentic. “It can’t be just words,” he said. “This is the true test of whether Democratic leaders have learned from past mistakes which have cost them control of the House.”

Running on the Republican ticket is Rick Saccone, a Pennsylvania state house member who has openly paralleled himself to Trump with his pro-gun, pro-veteran, anti-ObamaCare platform.

“I was Trump before Trump was Trump,” Saccone told radio station WESA earlier this month. “I ran on that agenda in 2010. It’s the same agenda — it’s the people’s agenda. The president just nationalized it.”

Trump’s approval rating is currently at 32 percent, according to a recent Pew poll, but you wouldn’t know it in this district where political signs supporting the president still abound. Still, anti-Trump Democrats turned out in force on Election Day this year, helping candidates like Ralph Northam, the next governor of Virginia, soar towards victory. The same could happen here in March.

Kyle Kondik, the managing editor of the University of Virginia’s Center for Politics, is dubious that a Republican will lose this district. “We rate this special election as ‘likely Republican.’ This is a district the party should be able to hold, but I’m very curious about the margin and whether the Democrats can really compete,” Kondik said.

One thing’s for sure: Whichever party loses will consider it a huge blow.

“A loss in the special election, in a very favorable electoral climate and against a Trump-backing candidate, would be a major embarrassment for Democrats,” Altmire said.

That’s especially true because this one could tell the future.