CARNEGIE, Pa. (AP) -- A special congressional election in Pennsylvania wasn't pegged as a close race when Republican Tim Murphy resigned last fall amid a sex scandal. Now, Republicans are scrambling to hold onto the seat in a district President Donald Trump dominated in 2016.
Polls suggest Democrat Conor Lamb could well pull an upset Tuesday over Republican Rick Saccone. If he does, it will sound new alarm bells for Republicans trying to defend their 24-seat House majority.
What to watch as votes are cast and tallied:
Outside Republican groups have spent about $10.7 million trying to help Saccone, a 60-year-old state lawmaker and Air Force veteran who's struggled to raise money and excite voters beyond his social conservative base. Lamb, a Marine veteran and former federal prosecutor, has outraised Saccone by more than 3-to-1, blanketed television and crisscrossed the district more aggressively than the GOP nominee.
Well before Tuesday, Republicans were blaming the tight race on Saccone's lackluster performance as a candidate.
"Anyone who wants to know why this is a race should watch 30 seconds of Rick Saccone and 30 seconds of Conor Lamb," says Corry Bliss, who runs a Washington-based political action committee that's aligned with House Speaker Paul Ryan, R-Wis. Trump picked up on a similar theme, commenting on Lamb's looks at a Saturday rally with Saccone. "I think I'm better looking than him," Trump said.
If Saccone hangs on, look for Trump to congratulate himself, while GOP strategists like Bliss credit their attacks on Lamb as House Minority Leader Nancy Pelosi's puppet. If Saccone loses, GOP forces will insist it's his fault. In either case, the way the campaign has played out offers Republicans warning signs ahead of November.
TRUMP EFFECT AND NATIONAL MOOD
While Washington Republicans talk about the race as a local anomaly, the national mood can't be ignored. White, working-class voters across the Rust Belt were critical to Trump's victory in 2016. If they're disillusioned with Republicans or unmoved by Trump's appeals to vote, that spells trouble for the party in the midterm elections in November.
Trump's footprints are all over southwest Pennsylvania. He's tweeted for Saccone and twice campaigned for him. Vice President Mike Pence, White House adviser Kellyanne Conway and Donald Trump Jr. also have made cameos.
But it's not at all clear that such campaigning persuades Trump voters to vote for someone other than Trump. Saccone may borrow the Trump slogan -- "This campaign is about something bigger than any of us ... making America great again!" he roared at a Saturday rally -- but he hasn't shown signs of tapping into the 2016 enthusiasm on the right. That momentum, it seems, has swung to the left -- and that frees up candidates like Lamb to aim for the middle.
UNIONS, TARIFFS AND OLD LOYALTIES
In these aging industrial communities, Republicans have benefited from organized labor's declining force in Democratic politics. The AFL-CIO estimates there are 87,000 votes from union households in Pennsylvania's 18th district, around a fifth of the electorate. That number includes about 17,000 steelworkers.
Labor is looking to Lamb to score big with that group and offer the movement signs of a comeback that could sway key Senate and governor's races this fall.
Saccone has been a union foe at the statehouse -- a break from the union-friendly Murphy, whose labor backing was a key reason Democrats couldn't topple him. Lamb told union workers Sunday they'd "been the heart and soul of this campaign."
Both candidates back Trump's new plan to impose steel and aluminum tariffs. Saccone, meanwhile, says rank-and-file laborers care more about tax cuts and low regulations than endorsements: "I'll take them any day over the union leadership backing my opponent."
OLDER VOTERS AND TAX LAW
The race will be the first major test of how the new tax law is playing with voters.
Saccone backs the Republican tax overhaul as a boon to workers' and the economy. Lamb echoes national Democrats who have labeled it a giveaway to large corporations and the wealthy. But he adds layers to the argument, criticizing the $1.5 trillion price tag.
Playing to fiscal moderates, he says future generations with inherit more debt. Playing to baby boomers and even older voters -- a key part of midterm electorates -- he says Republicans will use exploding deficits as an excuse to cut Social Security and Medicare. It's been effective enough that national Republican ads have shifted away from the tax debate in recent weeks.
A Lamb victory could accelerate his arguments in other districts and further worry Republicans about their plans to run unapologetically on the tax law.
Republicans' planned line of attack in 2018 is to cast Democrats as out of touch and link their nominees to Pelosi, the Californian who has been a GOP target for more than a decade. Watch Pittsburgh television for an hour or so and you'll hear an ominous voice warning that Conor Lamb "isn't one of us." It worked last year in a suburban Atlanta House race where Democrats spent record sums only to watch Jon Ossoff, another young, aggressive candidate, lose.
But Lamb has offered a potential antidote. He says he wouldn't vote for Pelosi for party leader. He opposes significant new gun regulations (and reminds voters in one ad that he "still loves to shoot" long after his Marine days). He generally talks about Trump only when asked. Lamb has tried to flip the script by linking Saccone to "the Paul Ryan budget" and cuts to Medicare.
As with the tax argument, Democrats running outside liberal strongholds may export those tactics if Lamb wins -- and even if he loses by a narrow margin.