President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE will touch down in Pennsylvania on Thursday, where he’ll make an appearance in the Pittsburgh-area district that’s home to the next high-profile special House election.

Trump is scheduled to give a speech at a local manufacturing plant — not to hold a campaign event for GOP state Rep. Rick Saccone, who is running in the March 13 special election and is expected to be in the audience.

But Trump’s appearance in the district, coupled with reports that Vice President Pence will travel to the district in the coming weeks, underscores the heavy investments Republicans are making to prevent Democrats from pulling off another special election upset.

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Pennsylvania’s 18th District seat is now vacant thanks to former Rep. Tim Murphy Tim MurphyBiden receives endorsements from three swing-district Democrats A federal abortion law might be needed Female Dems see double standard in Klobuchar accusations MORE’s (R) resignation, sparked by allegations surrounding an affair. Murphy had long faced little electoral opposition in the district, a stretch of suburban and rural areas surrounding Pittsburgh.

Democrats have the registration advantage in the overwhelmingly white congressional district, and can count on support from local unions. But the more conservative voters still lean heavily in favor of the Republican Party, and the district lacks the strong minority population that Democrats have mobilized to boost their vote share in recent wins.

Aware of the implications of how another Democratic upset would affect GOP momentum going into the 2018 midterm elections, Republicans are flooding the district with resources.

Trump will speak Thursday at H&K Equipment, a manufacturing company in the small town of Coraopolis. While Trump is giving the speech in his official capacity as president, the decision to come to the district is a clear boost to Saccone, both in drawing national Republican attention to the race and mobilizing Trump supporters in the district.

Trump won the district by almost 20 points during the 2016 election, an improvement on 2012 GOP nominee Mitt Romney Willard (Mitt) Mitt RomneyMomentum growing among Republicans for Supreme Court vote before Election Day Toobin: McConnell engaging in 'greatest act of hypocrisy in American political history' with Ginsburg replacement vote The Memo: Court battle explodes across tense election landscape MORE’s 17-point margin.

Even as Trump’s favorability ratings drop nationwide, including in Pennsylvania, Republicans are confident his appearance will help motivate their voters.

“The advantage of the president going there is that it’s about turnout in a special election. The president out there will certainly help with Republican turnout and it will help with the Trump Democrats who came out to support the president [in 2016],” said Vince Galko, a veteran Republican strategist in Pennsylvania.

The Trump visit coincides with a concerted national effort in the district.

National groups have spent more than $1 million peppering the airwaves with advertising, with more spending on building out a ground game for Saccone.

The Congressional Leadership Fund, a top GOP super PAC aligned with Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (R-Wis.), has opened two field offices on either side of Pennsylvania’s 18th District with plans for 50 doorknockers.

The bulk of the Congressional Leadership Fund’s ads focus on tying Democrats to House Minority Leader Nancy Pelosi Nancy PelosiSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Trump is betting big on the suburbs, but his strategy is failing 'bigly' Trump orders flags at half-staff to honor 'trailblazer' Ginsburg MORE (D-Calif.). Democrat Conor Lamb has already sought to neutralize that attack, announcing that he won’t support Pelosi as leader if he’s elected. Lamb has also sought to turn the tables on Saccone by targeting Ryan’s role as Speaker, accusing him of “coming after” Social Security and Medicaid.

But Republicans aren’t buying Lamb’s distancing from Pelosi, using her as shorthand for the Democratic congressional agenda.

“Conor Lamb is literally just another vote on the Pelosi line,” said Brian Baker, who helps run the conservative outside groups Ending Spending Action Fund and 45Committee.

Ending Spending has already dropped $600,000 on a positive ad in support of Saccone that aired on television, radio and digital platforms. And 45Committee went up last weekend with a spot attacking Lamb for his stance on the recent GOP tax plan, putting his picture on screen next to Pelosi’s in a $500,000 buy.

Saccone is getting help from Washington, too. He spent Wednesday fundraising in Washington, and is slated to return in February to seek more money.

Recent Democratic improvements in other traditionally safe GOP areas, the overwhelming Democratic advantage in House generic ballot polling and Saccone’s historically lackluster fundraising gives Democrats a unique opening in the district.

Democrats overperformed in last summer’s special House elections in safe Republican districts. The party also had a huge upset in December’s special Senate election in Alabama, though the GOP nominee faced multiple sexual misconduct allegations.

In another sign the headwinds are getting stronger for Republicans, Democrats unexpectedly won a special state Senate election in rural Wisconsin on Tuesday.

“One special election alone is not predictive of the midterms. However, the sum total of the elections we’ve seen since the Trump presidency started paints an undeniable picture of voters rebelling against the people that seized power in Washington,” said Democratic strategist Jesse Ferguson.

Lamb’s campaign booked $100,000 in television ads over the next week to help combat the massive GOP spending. But national groups haven’t yet followed suit.

NextGen America, the group led by Democratic billionaire mega-donor Tom Steyer, told The Hill it hasn’t finalized whether it'll get involved in the race. Steyer recently said he’ll spend $30 million to help Democrats flip the House and boost turnout among young voters, with Pennsylvania among the 10 states Steyer’s group plans to target.

Lamb also has support from the Pennsylvania chapter of the AFL-CIO, which could play a useful role in helping to make inroads among the district’s union voters.

Ferguson said the wait-and-see strategy makes sense here, chiding the GOP for resorting to “parachuting the president” into a district he won handily in 2016.

“The fact that Republicans have to launch a rescue mission in an overwhelmingly Trump district before Democrats even step up their engagement tells you what they’re confronting here and previews what they’ll confront in the midterms,” Ferguson said.

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