The tight-as-a-tick race to replace disgraced 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 (R) in a suburban and exurban Pittsburgh district Tuesday is jolting already nervous Republicans who worry their majorities may be wiped out in a wave election this fall.

With 100 percent of precincts reporting, Democrat Conor Lamb, who has declared victory, leads Republican state Rep. Rick Saccone by two-tenths of a percentage point, a little more than 600 votes. Several thousand absentee votes from across the district remain to be counted, though they are not likely to change the outcome.

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Even without a declared victor, the results illustrate the challenge Republicans face even in a district 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 by more than 20 percentage points just 16 months ago: Voters who were motivated to show up for Trump are far less motivated to show up for other members of his party, even when Trump himself implores them to vote.

“We’ve known for a long time that this has been a tough political climate, but given the make up of the district this puts it in very stark terms,” said Doug Heye, a former communications director at the Republican National Committee.

The GOP's conundrum is one with which Democrats are intimately, and painfully, familiar.

After President Barack Obama Barack Hussein ObamaDemocratic Senate campaign arm outraises GOP by M in August A federal court may have declared immigration arrests unconstitutional Blunt says vote on Trump court nominee different than 2016 because White House, Senate in 'political agreement' MORE built winning coalitions in both 2008 and 2012 that swept fellow Democrats to big wins, millions of the voters who sent Obama to the White House sat on their hands in midterm elections in 2010 and 2014 — elections in which Democrats lost control of the House, the Senate and nearly a thousand state legislative seats across the country.

“What they're dealing with is something we dealt with in '10 and '14, which is a very depleted base with no enthusiasm that’s non-transferrable,” said Matt Canter, a Democratic strategist who worked for the Democratic Senatorial Campaign Committee during the 2014 midterms.

Midterm elections are fundamentally different than presidential contests, and both sides struggle to turn out occasional voters, even those who favor their side.

But in recent years, the party in power has struggled to leverage its winning presidential coalition in part because the party out of power is more motivated to register their opposition.

“Every president has this issue of, you're not on the ballot but everybody's running against you,” said Bryan Lanza, a Republican strategist who served as Trump's deputy communications director during the 2016 campaign.

Though Republican strategists have made clear they will pin the blame for the close result — win or lose — on Saccone, who they say ran a lackluster campaign, Trump made himself a factor in the race.

The president appeared at a weekend rally with Saccone, and top Trump surrogates — including Vice President Pence, Donald Trump Jr. Don John Trump'Tiger King' star Joe Exotic requests pardon from Trump: 'Be my hero please' Zaid Jilani discusses Trump's move to cancel racial sensitivity training at federal agencies Trump International Hotel in Vancouver closes permanently MORE and Ivanka Trump Ivana (Ivanka) Marie TrumpTrump, Biden vie for Minnesota Trump luxury properties have charged US government .1M since inauguration: report Ivana Trump: Ivanka could 'definitely' be first female president MORE — all campaigned with Saccone.

The heavy involvement of Trump administration officials is a sign the president believes only he can reanimate his own base in order to benefit his party in this November's midterm elections, Lanza said. Like Obama, who faced low approval ratings but still traveled to heavily Democratic areas to turn out voters in 2010 and 2014, Trump too plans to be an active presence on the campaign trail.

“What you have is an administration that recognizes the challenge ahead, and they're putting all their athletes on the field,” Lanza said.

Trump’s approval ratings, however, are far worse than Obama’s, which were in the mid-40s in those midterm contests. The fact that Saccone fell so short of Trump's 2016 margins — even with the late help from Trump — underscores the challenge Republicans face in replicating the president's winning coalition.

“The problem is Donald Trump's approval rating,” said Heye, a frequent GOP critic of the president.

Some observers said the Obama voters who registered their disapproval with Democrats when Obama wasn't on the ballot are the same voters now registering displeasure with Trump and the GOP.

“I think part of the Obama coalition and part of the Trump coalition are the same people — largely non-college voters who feel like they aren't sharing in the economic success of our country, and they're eager for change,” said one Democratic strategist intimately involved in House races during the Obama years.

“In 2008, they voted for Obama as a change agent, and they bought into the hope and optimism he conveyed. In 2016, they voted for Trump, many of them holding their nose, because they thought maybe electing someone who was outside the political system would shake things up and bring them a better future. That isn’t happening for them.”

Others said Tuesday's election will have a more immediate detrimental impact on the GOP this year. Heye said the results might push more Republican members of Congress to decide against what increasingly looks like a difficult reelection fight.

“It shouldn’t be any surprise if we see a few more Republicans in the House announce retirement,” Heye said.