To witness the Republicans in full panic mode, check out the action in the southwest corner of Pennsylvania, where they’re performing emergency triage on a congressional seat that should be the picture of health.

Donald Trump flew up yesterday to ballyhoo Rick Saccone, the Republican candidate in the March 13 special election: “He just met me at the plane, and he’s here someplace … Rick is a great guy. He’s a special person.” Trump, of course, doesn’t know the first thing about this guy, and in a normal year he wouldn’t need to, because the 18th Congressional District, gerrymandered by state Republicans to resemble a gun, is solid Republican turf. Trump won the district’s presidential vote by 20 points, and Tim Murphy, the district’s most recent Republican congressman, won eight straight elections — the last two, without an opponent.

So why, all of a sudden, did Trump feel compelled to show up? Why is Mike Pence planning to go? Why are various Trump Cabinet members planning to go? Why has the Republican National Committee sent field staffers? Why has Paul Ryan’s super PAC opened a district office and dispatched 50 people to knock on doors? Why is a billionaire-financed conservative group planning to spend a million bucks on TV ads? Why is an outside pro-Trump group planning to kick in half a million for its own media blitz?

Because the GOP is terrified of suffering another electoral humiliation — not necessarily a defeat, given the district’s demographics, but an election night nail-biter that refuels Republican fears of a blue tsunami in the November midterms.

Their fears are justified. Three nights ago, Democrats won a special state Senate election by 11 points in a rural Wisconsin district that Trump won in 2016 by 17 points; in the words of conservative Charlie Sykes, a former radio host, that result has hit the GOP “like an electric shock.” Four weeks ago, Democrats won the special U.S. Senate election in Alabama. Eight weeks ago, they easily won the gubernatorial elections in Virginia and New Jersey. Democrats lost all the special House elections in 2017, but the margins in those solidly red districts were unusually narrow. And since ’16, Democrats have flipped 34 state legislative seats. Sykes says, “Trump is the subtext in all these races.”

Now comes the imminent Pennsylvania contest, which was made possible by the sudden ’17 resignation of Congressman Tim Murphy, who always lauded his family and opposed abortion — but was outed for allegedly telling his extramarital mistress that, if pregnant, she should get an abortion. Saccone, a veteran state legislator who likes to boast that he “was Trump before Trump was Trump,” has stepped in, betting that the locals still love Trump. But unlike Murphy, he’s not running unopposed. The Democrats are fielding a candidate straight from central casting, a young telegenic ex-Marine and former prosecutor named Conor Lamb. And he’s raising more money than Saccone. In a district where Republicans traditionally haven’t needed to raise a cent.

The danger for Saccone — and, by extension, for Trump — is two-fold. The district is heavily populated by blue-collar whites who bought Trump’s ’16 con about the return of factory jobs and the promise of infrastructure projects. But nothing has happened on either front. The district’s union members need only look to their brothers and sisters at the Carrier manufacturing plant in Indiana, where Trump trumpeted a deal to save their jobs — and where 1,500 are now out of work, with 200 clocking out forever just last week. (A union president at Carrier says: “The workers that I talk to feel betrayed, because he made promises that he didn’t keep.”) Plus, Saccone in Harrisburg has sponsored anti-union bills.

The other danger is in the district’s Pittsburgh suburbs — where college-educated white women aren’t likely to back any candidate who’s tied to Trump. Thanks to Trump, the GOP has been hemorrhaging those women — as evidenced in polls (66 percent disapproval of Trump) and in recent election results, most notably Virginia. And I doubt that these women will brighten their view of Trump in the wake of the news that his porn-star babe spanked him with a Forbes magazine.

All told, says Pennsylvania Congressman Charlie Dent, a moderate Republican who’s bailing this year, the southwestern district “should go Republican, but in this environment one can never take anything for granted.”

Which is why Trump and his beleaguered party are pumping so much political capital into a place that normally needs nothing. Who knows, maybe they’ll just tie Conor Lamb to Nancy Pelosi and maybe that’ll be enough. But they know darn well that a loss or tight win in a Trump fiefdom will be the equivalent of a four-alarm fire, prima facie evidence that few Republican seats should be considered safe in 2018.