ELIZABETH TOWNSHIP, Pa. Democrat Conor Lamb defeated Republican Rick Saccone in a special election for Pennsylvanias 18th Congressional District, a GOP-held seat where Donald Trump won by nearly 20 percentage points .

Lambs projected win comes the day after polls closed, as initial counts were too close to call on Tuesday night. As of Wednesday evening, Lamb held a narrow 627-vote lead, according to both The New York Times and NBC . There are still 500 outstanding provisional, military and absentee ballots to be counted between the four counties in the district, but it appeared unlikely that the election results could change absent further unexpected developments.

Pennsylvania does not have an automatic recount in elections on the congressional-district level, but Saccone can still petition for one within five days of the counties completing their vote tabulations.

The win is a massive upset by Democrats reflecting the heightened enthusiasm of the partys liberal base and the general dissatisfaction of many voters with the Trump presidency.

The party now has the wind at its back ahead of the midterm elections in November when Democrats hope to wrest control of Congress from the GOP.

The congressional map for potentially competitive races has just gotten a whole hell of a lot bigger, said Mike Mikus, a western Pennsylvania-based Democratic consultant. If Im the Republicans , Im terrified. If Im the Democrats, Im very energized looking toward November.

Republicans have downplayed the broader significance of the race, arguing that it could be explained almost entirely by Saccones flaws as a candidate, or more recently, Lambs alleged willingness to run a Republican-lite campaign.

But the election results show that the GOP needs to do more to appeal to moderate suburban voters, regardless of who the candidate is, said Mark Harris, a Pittsburgh-based Republican strategist.

Its not a good sign, he said. We have to run better campaigns that have messages that are going to resonate with voters regardless of their opinion of the president.