WASHINGTON — Although Pennsylvania’s 18th congressional district is landlocked, it may well be in the path of a big blue wave.

The once solidly Republican southwestern Pennsylvania district, which Donald Trump won easily over Hillary Clinton in 2016, is holding a special election Tuesday, and Democrat Conor Lamb holds a surprising lead in polls. A Monmouth University survey released Monday showed Lamb with a six-point lead over Republican candidate Rick Saccone — in a district that Trump won by 20 points.

Lamb, a 33-year-old former Marine and Saccone, 60, a state legislator, are competing for a seat previously held by Rep. Tim Murphy, a Republican, who was brought down by a sex scandal. Murphy, who was avowedly pro-life, resigned in October after reports that he asked his mistress to obtain an abortion.

This will be the final election in the Keystone State’s 18th congressional district after the Supreme Court ordered a redrawn map of Pennsylvania congressional districts earlier this year. That new map will split the current 18th district into four different ones.

So why are members of both parties so eager to win a race in a white, blue-collar district that won’t even exist by the fall?

With midterm elections just months away, the western Pennsylvania district may serve as a key indicator of which party has more momentum going into November. Whichever candidate wins, the closeness of the 18th district’s race is itself a blow to Republicans, who may be forced to spend time and financial resources defending districts that Trump won by large margins.

Republicans have spent an astounding $10 million to try to keep the district in their column, but Lamb has maintained a slight lead with Democrats having spent a little more than $1 million.

Moreover, a loss in Pennsylvania would be just the latest major blow to Republicans’ electoral ambitions after losing a 2017 senate race in ultra-red Alabama, as well as the governorships in Virginia and New Jersey. However, if Saccone wins, it will mark the sixth Republican win in a Congressional special election since Trump’s inauguration — meaning that the GOP may have some momentum of its own.

Tuesday night’s outcome will be a critical indicator of the electoral challenges that lie ahead for both parties; here are a few key things to watch.

Turnout questions

Democrats have traditionally struggled to turn out their voters during midterm elections, but the president’s remarkable unpopularity may be enough to motivate Pennsylvanians to head to the polls.

That strategy has already seemed to work in a March 7 Texas Senate primary, where Democrats doubled their turnout rate compared with 2014.

“What’s happening in Texas is part of a national trend,” said Democratic National Committee chair Tom Perez in a statement after the primary. “All across the country, Democrats are competing and winning in deep-red states.”

A move to the center?

At a time when both parties seem to be getting more extreme — Republicans, of course, nominated an immigration hardliner for president, and Democrats nearly nominated an avowed socialist, Sen. Bernie Sanders of Vermont — Lamb is a proud centrist.

While coastal Democrats are calling for bans on semiautomatic rifles, Lamb’s first campaign ad showed the ex-Marine shooting an AR-15 rifle. Lamb has also said that he is personally pro-life, although he has said he would not support laws further restricting the right to choose.

Republicans have aired ads in the district linking Lamb to House Minority Leader Nancy Pelosi D-Calif, but Lamb himself has gone on record saying he would not support her reelection as leader.

A Lamb victory would be a sign that voters are much more amenable to moderate candidates than recent conventional wisdom has held. On the other hand, at a time when the gun debate has taken center stage for many voters after the mass shooting at a Parkland, Fla., high school that killed 17, Lamb’s views may frustrate Democrats who are eager for gun control reform.

Age is just a number

Democrats have been criticized for being an older party; most of the lawmakers considered likely to run for the 2020 nomination — Elizabeth Warren, Joe Biden, Bernie Sanders — are 65 or older.
In February of last year, former DNC chair Howard Dean acknowledged this, telling MSNBC that the party’s “leadership is old and creaky, including me.”

The Democratic Party selected Joe Kennedy III to give the State of the Union response in January, which was widely seen as an attempt to give the spotlight to a younger Democrat.

Lamb, at 33, might be the first in a younger generation of Democrats to make a name for himself on the national stage. Saccone, 60, is nearly twice his age.

Blue collar, red state

The conventional wisdom about Trump’s 2016 victory is that he won the Electoral College by enticing blue-collar voters that normally voted for Democrats over to his side. That theory will be put to the test today, as many of the voters who did rally for Trump will be going to the polls again — and possibly electing someone on the other side of the aisle.

Union activists have been working tirelessly across the district, canvassing on Lamb’s behalf and encouraging union members and their families to turn out for him. Both Lamb and Saccone have spoken out in favor of the president’s steel and aluminum tariffs, which Trump himself touted in a visit to the district over the weekend.

Was Trump’s 2016 Pennsylvania win a fluke or a sign of significant ideological change among blue-collar voters? Tuesday’s election may shed some light on the question.

Trump’s kiss of death?

Trump’s trip to Pennsylvania’s 18th was, predictably, light on Saccone and heavy on Trump himself. The president spoke at a rally outside Pittsburgh, briefly endorsing Saccone before launching into a lengthy tirade about Oprah, gangs, and his reelection slogan.

Despite the president’s ostensible show of support for the Pennsylvania Republican, he seemed also to rebuke Saccone for the closeness of the race, telling the crowd: “This guy should win easily.”

Saturday’s rally was an early picture of what the president might look like on the campaign trail for midterm elections this fall. But whether the rally invigorated Saccone supporters or merely distracted them will be difficult to tell until returns come in.

Votes from tax cuts and steel

Tuesday’s election will be the first congressional election since the Republican tax plan was signed into law late last year. Just as the race might be seen as a referendum on Trump, therefore, it may also be a referendum on Republicans’ flagship policy achievement since the president took office. Republicans across the country are likely to be campaigning on the tax reform bill, which they say will raise wages and decrease unemployment.

Whether that message has resonated with voters is less clear. A Quinnipiac poll from December found that just 29 percent of voters approved of the tax cut plan, although 67 percent of Republicans did. Subsequent polls show the GOP tax law is gaining in popularity. Tax cuts may be a key factor in motivating Republican voters to the polls; conversely, on-the-fence moderates may decide to vote Democrat or sit out altogether.

The president’s proposed steel and aluminum tariffs are also a major topic of conversation at Pennsylvania rallies. But with both Democrat and Republican in favor, it is unlikely that the outcome of Tuesday’s vote will provide as much clarity about tariffs as it could about the tax bill.