Democrat Conor Lamb is days away from a possible win in a long-held Republican congressional district that went for President Trump by 20 points.

If Lamb wins — a once-inconceivable feat — it will be the first national victory for Democrats in 2018, providing further evidence of an impending “blue wave.”

The race, once considered a pulse check on Trump, is now neck-and-neck, with Lamb up slightly in the polls. Fearful of losing the southwest Pennsylvania seat, Republicans have poured nearly $10 million toward boosting GOP candidate Rick Saccone.

By November, the district, which borders West Virginia and includes the Pittsburgh suburbs, may not even exist. But the outcome of the March 13 special election will have far-reaching implications. If Republicans lose, they will be in cleanup mode, rushing to mitigate the damage to their brand. For Democrats, a win, or near win, sends a signal to their base that they can come out on top in deeply red districts.

“A near win shows you we’re over-performing in these districts — this is an R+11 district, we’re not supposed to be competitive here,” said Rep. Mike Doyle, D-Penn. “[Republicans are] certainly not happy about what they’ve been forced to spend not to be embarrassed.”

“If we win it is a real sign of the coming wave,” said Rep. Brendan Boyle, D-Penn.

Careful not to tie himself to national Democrats, Lamb, a Marine veteran, has kept a tight grip on his campaign and the money flowing through it. The Democratic Congressional Campaign Committee has offered little help, deferring to Lamb at every turn.

Early on, Lamb vowed to not vote for House Minority Leader Nancy Pelosi. Sticking to a tried and true strategy, Republicans tethered Lamb to the San Francisco Democrat at every turn, but Lamb’s centrist image has remained intact.

“Having yourself separated from Washington is a positive,” said Rep. Tim Ryan, D-Ohio, adding that if Lamb wins it could provide Democrats with “a framework” and “messaging platform for our other candidates to replicate.”

Republicans haven’t hidden their unease about the race as they’ve watched it slowly slip away. Many have been quick to place blame on Saccone, who they deem a lackluster candidate unable to effectively fundraise.

He’s also lost the image battle to Lamb, a telegenic 33-year-old straight from central casting. Frustrated by Saccone’s performance, some Republicans have gone so far as to zero in on his mustachioed appearance.

"It's a porn stache,” said one Pennsylvania-based GOP strategist. “He should have lost the mustache."

"He's an ineffectual candidate,” the strategist said. “You're not going to change him appreciably, but you could have positioned him very differently.”

Every story about Lamb pointed out that he’s a Marine, the strategist lamented, but Republicans failed to communicate that Saccone too has a career in the military as an Air Force officer, and served in North Korea.

“They now kind of whine about, 'The media didn't tell that story,'" the strategist said. “The campaign has to tell that story.”

Lamb has dominated the airwaves in recent weeks. Saccone hasn’t kept pace, conspicuously absent and overly reliant on outside groups. The National Republican Congressional Committee and the Congressional Leadership Fund — a PAC backed by Speaker Paul Ryan — have spent in total roughly $7 million.

“I feel like we're in the game,” said Rep. Steve Stivers, R-Ohio, who chairs the NRCC. “It's going to be a fight, but I feel good about our chances now and his trend line is moving in the right direction.”

But few Republicans are as optimistic as Stivers. After throwing millions at a seat that will likely be gone in a matter of months, Republicans could have nothing to show for it. Neither candidate lives in the newly-constructed 18th District.

Doug Heye, a former communications director at the Republican National Committee, said the race is about much more than “who can claim momentum” or who will “have an extra vote for eight months.”

“If we lose that seat, the potential for there to be a small wave of other Republican incumbent retirements is very real,” said Heye.

The sizable impact a Democratic victory could have on the GOP’s morale didn’t escape Rep. Joe Crowley, D-N.Y., chairman of the House Democratic Caucus.

“It sends shivers down [Republican] spines everywhere,” the New York Democrat said. “It means that this is going to be a pretty good election year for Democrats.”