Come November, thanks to a recent re-drawing of Pennsylvania’s electoral map, the state’s 18th District is likely to disappear. Yet for the G.O.P., the stakes in Tuesday’s special election there couldn’t be higher. In a district where a Republican has run relatively uncontested since 2002, and where Donald Trump won by 20 points, Democratic candidate Conor Lamb is locked in a dead heat with Republican Rick Saccone, despite massive cash infusions from national party operatives—over $9 million between the N.R.C.C., the Congressional Leadership Fund, the R.N.C., and America First Action. Lamb’s ascendance, coupled with Saccone’s failure to launch, has terrified Republicans who see the race as a gauge for what’s to come. “If the Democrats were to prevail in western Pennsylvania, that would be quite an earthquake,” Representative Charlie Dent, a fellow Pennsylvania congressman retiring this year, told The New York Times. “If a strong pro-Trump district like this goes the other way, it would send a bad signal around the country in districts far more competitive than this one.”

Yet Saccone entered the race with some notable advantages. Along with the 18th’s voting history and the outsize amounts of money being spent there on his behalf, Republicans stood ready to deploy their heaviest hitters. Mike Pence and Ivanka Trump have both made appearances, and Donald Trump Jr., and Kellyanne Conway are scheduled to visit the district in the coming days. Trump himself will campaign there for the second time, despite the protestations of his advisers. Unlike candidates like Roy Moore and Ed Gillespie, Saccone had largely steered clear of the kind of vitriolic rhetoric that marked him as too closely aligned with the president. In fact, as New York’s Ed Kilgore notes, Saccone amounted to “a reasonably orthodox and scandal-free candidate with a decent résumé, running against a first-time” former prosecutor. There were, in other words, relatively few roadblocks in his path to the seat.

Despite the efforts of the national party, however, Saccone has proven startlingly resistant to outside help. According to Politico, he’s a poor fundraiser who frequently bucks the advice of Republican advisers and refuses to put effort into running a strong campaign. Recent internal-polling data shows that just 47 percent of voters in the district view Saccone favorably—3 percentage points lower than Trump. Nor have Republicans been shy about voicing their dissatisfaction. “In a tough political environment, candidate quality matters more than ever,” Ken Spain, a former N.R.C.C. senior aide, told Politico, an echo of the Establishment’s argument against alleged pedophile Moore. “In an anti-GOP year—which this is shaping up to be—the Republican candidates will need to run much stronger campaigns or be prepared for the national party to cut them loose.”

But a high-profile, Alabama-style loss, particularly in a pro-Trump region, will only contribute to the growing sense that the president is toxic to the Republican party. The fact that Lamb has proven unexpectedly adept at fundraising, out-raising Saccone nearly five to one, only underscores that perception, fueling the so-called “blue wave” that Republicans fear will decimate their majorities in Congress. “If he wins, you’re going to see probably another half a dozen Republicans say they’re not running again,” former V.P. Joe Biden told The New York Times while visiting the district.

Biden added that Lamb’s campaign could hasten the party‘s efforts to return to its roots, “getting back working-class people supporting us again.” And, indeed, Lamb, who is less progressive than a traditional Democratic candidate, has voiced his support for Trump’s steel tariffs, which could play well in the industrial district. The telegenic Ivy League graduate and former Marine is also in favor of Republican-style gun control, and has taken pains to distance himself from Democratic leadership, openly calling for Nancy Pelosi to step down as House Minority Leader. He also, unusually for a Democrat, has refused to bash Trump during his campaign, and has eschewed bringing in big-gun Democrat surrogates (save for Biden, the party’s dedicated blue-collar whisperer). “I don’t really care what the future of the party looks like,” he told The Atlantic, a shrewd move for a Democrat running where voters are generally happy with the state of the Trump-led economy).

If Lamb wins the district, it will be a devastating blow to Republicans. But even a near loss, which some experts hold is the more likely scenario, will leave them rattled. The G.O.P. fears that either scenario will reflect poorly on the president, whose failure to adhere to the party’s preferred talking points—glorious tax cuts, a booming economy—they believe landed him in this precarious seat in the first place. “He is making losing the majority more likely,” a longtime Republican operative told CNN. “He is creating the reality for his impeachment by the House. Hill Rs are flabbergasted. And when Rs lose the safe PA seat, panic will become epidemic.”