CANONSBURG, Pa. — Democrat Conor Lamb looks likely to win Pennsylvania’s close special election, giving his party a significant morale boost heading into the battle for the House majority this fall.

President Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE won the district by nearly 20 points in 2016, but Lamb has reversed Democratic fortunes in the area. He leads Republican Rick Saccone by more than 500 votes in the latest count, even after Republicans dumped more than $10 million into an attempt to hold the reliably Republican district.

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Lamb’s expected victory has caused panic within the GOP, as some in the party are already warning that it’s the latest sign of a midterm wave.

Here are five takeaways from Lamb’s upset win:

More evidence of a blue wave

More Republicans are starting to sound the alarm about the future of their House majority.

Trump’s unpopularity is pushing seats that had once been considered safe into riskier territory. Democrats need to win 24 seats to take back the House.

Lamb outperformed Hillary Clinton Hillary Diane Rodham ClintonBiden leads Trump by 36 points nationally among Latinos: poll Democratic super PAC to hit Trump in battleground states over coronavirus deaths Battle lines drawn on precedent in Supreme Court fight MORE’s 2016 numbers in the district and significantly outraised his opponent, giving Republicans pause as they consider how to maintain their majority.

"This is a wake-up call. If you're getting outraised, this is a wake-up call,” National Republican Congressional Committee chairman Steve Stivers Steven (Steve) Ernst StiversBusiness groups back pandemic insurance bill modeled on post-9/11 law National Retail Federation hosts virtual 'store tours' for lawmakers amid coronavirus Stronger patent rights would help promote US technological leadership MORE (Ohio) said Wednesday, a source in a closed-door meeting of House Republicans told The Hill. “Prepare to bear down."

Before Lamb’s win, national Democrats were targeting 101 GOP-held districts in the fall. Now the victory gives more credibility to the idea that Democrats can start targeting seats that were once considered out of reach.

Strategists in both parties expect Lamb’s success to prompt another wave of GOP retirements, leaving the party defending more vulnerable seats without the advantage of incumbency.

“This is not a good result for the GOP. Look for more retirements to come,” Doug Heye, a former Republican National Committee spokesman, tweeted Tuesday night.

Tax cuts and Pelosi attacks won't work everywhere

Republicans largely focused their messaging on promoting the GOP tax-reform plan and painting Lamb as a rubber-stamp for House Democratic Leader Nancy Pelosi Nancy PelosiAs families deal with coronavirus, new federal dollars should follow the student Sunday shows - Ruth Bader Ginsburg's death dominates Hypocrisy rules on both sides over replacing Justice Ginsburg MORE (Calif.).

But Lamb’s win proved those strategies won’t resonate everywhere.

Outside Republican groups like the Congressional Leadership Fund and the National Republican Congressional Committee spent millions to boost Saccone, relying on the tax plan to drive votes.

But as Saccone continued to slip in the polls, their closing arguments centered more on attacking Lamb for negotiating plea deals as a prosecutor and connecting him to contentious issues like sanctuary cities and illegal immigration.

Tuesday’s results have emboldened Democrats who believe that Lamb’s strong performance is proof that the GOP can’t lean too heavily on the tax plan as the centerpiece of its midterm strategy.

Meanwhile, Republicans caution against reading too much into Tuesday’s results. In their minds, Saccone’s flaws overshadowed much else and the party’s incumbents will likely have far stronger operations than he did to define their own messages.

Republicans have come to rely on tying Democrats to Pelosi, but that strategy didn’t turn off enough voters in Pennsylvania — in part because Lamb distanced himself from the top Democrat.

Lamb took the unusual stance of almost immediately announcing that he wouldn’t back Pelosi for Democratic leader if elected, even running an ad to drive the point home.

Lamb was able to blunt the GOP attacks about Pelosi, which could open the door for more Democratic candidates or lawmakers to come out against her.

But Lamb’s strategy won’t work for every Democrat. Not all Democratic candidates will be able to separate themselves from Pelosi, which will make them vulnerable to attacks from Republican groups.

The fact that Lamb had to come out against Pelosi is the rare bright spot for Republicans in Tuesday’s results.

“Nancy Pelosi is a liability to Democratic candidates. Lamb had to distance himself from Pelosi and reject her,” GOP strategist Garrett Ventry told The Hill.

GOP trouble in Trump country

Tuesday’s special election found a Republican candidate struggling to repeat Trump’s success in what should have been a solidly Republican district.

But it’s difficult for Republicans to mobilize the voters that carried Trump to victory in 2016, when historically the party in power loses seats in a midterm and is less motivated than the opposition.

Trump traveled to the district twice, but that wasn’t enough to pull Saccone over the finish line.

During a weekend rally days before the election, Trump sang Saccone’s praises. He called him “an extraordinary guy” and said Saccone will easily win on Tuesday. And others close to the White House deployed to the district in a last-ditch effort to save Saccone.

While Trump wasn’t on the ballot, the race was a test of whether other Republicans could draw on the votes who helped hand Trump his surprise 2016 win. And growing unpopularity has spurred an enthusiasm gap that buoyed Democrats in recent elections.

A boost for Biden 2020

Lamb isn’t the only Democrat who won big Tuesday night in Pennsylvania. The upset win also provides more fuel for a potential presidential run for former Vice President Joe Biden Joe BidenBiden leads Trump by 36 points nationally among Latinos: poll GOP set to release controversial Biden report Can Donald Trump maintain new momentum until this November? MORE.

Biden, who’s exploring a 2020 bid, has frequently hit the trail for red-state Democrats and campaigned alongside Lamb twice in the final weeks of the race.

Biden was one of the few national Democrats who campaigned in the district, as candidates in red or swing districts look to keep Washington and the national party brand at arm’s length.

Biden has been an effective surrogate for connecting with rural and working class voters. Now Lamb’s victory demonstrates that Biden can help win back those voters — right as Democrats consider which 2020 primary hopeful will deliver them the White House.

Dems can break with litmus test and win

Democrats are facing an internal debate that has roiled the party since last year: a litmus test that candidates must support abortion rights.

Lamb, who is Catholic, was able to delicately navigate that issue without ruffling any feathers. He said he’s personally opposed to abortion, though he supports the right to choose. He recently told The Weekly Standard he’s not in favor of a 20-week abortion ban.

He also struck a more moderate tone on other hot-button issues.

Lamb’s first campaign ad featured a clip of him shooting an AR-15 at a gun range, and he didn’t engage in Democrats' calls for new gun policies following the deadly mass shooting in Parkland, Fla. But he supports strengthening the background check system.

Republicans concede that Lamb was a good candidate they say ran as “Republican lite.” But they argue that he was a unique case whose success will be hard for Democrats to replicate.

But Democrats say they have plenty more candidates like Lamb. After the win Tuesday, House Democrats’ campaign arm said there are 60 other Democratic House candidates whose military or national security credentials echo Lamb’s background.

Scott Wong contributed.