11:31 PM ET: Race too close to call. From Politico:

The Pennsylvania special congressional election is too close to call, with Democrat Conor Lamb leading Republican Rick Saccone, 49.9 percent to 49.5 percent — a margin of only 755 votes — with 99 percent of precincts reporting, according to The Associated Press, which said it would not declare a winner Tuesday night.

Thousands of absentee ballots are still outstanding. After those are tallied, the trailing candidate has the option to request a recount, according to state law.

Apparently there is no automatic recount. There would have to be a petition filed signed by 3 voters in each precinct within 5 days of certification of the vote in each precinct.

This Democratic PA lawyer who is knowledgeable about the process explains what happens now:

Before the Close Analysis

The PA-18 Special Election, in the western part of the state near Pittsburgh, should be a Republican cakewalk, considering Trump won the district by 20 points. (Note: This is the “old” district, not the new one the PA Supreme Court ordered for the November election.)

But it’s turned into what the polls suggest will be a close race. The polls close at 8 p.m. Eastern.

Republican Rick Saccone has run a lackluster campaign, while Democrat Conor Lamb is running as a conservative Democrat imposter, trying to shape himself as someone who is right on key issues. It’s a farce and a sham, but in a year when Democrats seem to have more motivation, it may dampen Republican turnout to have a Democrat who supposedly agrees with them on key issues.

Trump campaigned in the district, and Republicans put in the resources and manpower the Saccone campaign lacked.

If Lamb wins, it will dominate headlines for days or weeks and will be viewed as a precursor to Democrats taking back the House. If Lamb loses by low single digits, the spin will be that Democrats outperformed. The only way Republicans get spin out of this — as far as the mainstream media is concerned — is if Saccone wins by double digits.