Forget about absentee ballots, forget about recounts. For Republicans, the PA-18 congressional race was lost before the polls even opened. And for Democrats, the path to victory has been laid out—if they're smart enough to see it.

The district should have been nearly impossible to flip. As has been repeatedly noted, Donald Trump won it by 20 points just over a year ago, and the previous GOP congressman often ran unopposed. This district was drawn by Republican legislators to elect Republicans —which is why the Democrats new gerrymandering plan will wipe it off the map.

So whether Conor Lamb holds on by a decimal point or falls short by a handful of votes, this is already a win for Democrats because it shows potential candidates across the country that this is a year when nearly every seat could be in play. As former Hillary Clinton spokesperson Jesse Ferguson noted last night, there are 118 GOP districts where Trump got a smaller percentage of the vote than PA-18. In theory, every one of them could be a pick up based on Tuesday's results.

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In theory. In fact, the GOP was hurt by the weakness of their nominee Rick Saccone, and the scandal left behind by Rep. Tim Murphy—forced to resign when the socially conservative Republican was caught sending text messages to his girlfriend urging her to get an abortion. And there's one more factor, perhaps the most important one: The Democrats ran a strong candidate.

Much has been made of the fact that Democrat Conor Lamb "matches the district," as Democratic Party leaders put it. Running in Trump Country, he was pro-gun ownership (or at least not against it); "personally pro-life," as the saying goes—which in Lamb's case means he would still vote with Planned Parenthood; and he pledged not to back Nancy Pelosi for Speaker.

In other words, the Democratic nominee is someone who would have virtually no chance of making it through a Democratic primary. And that didn't happen by accident. He was picked by party leaders in a "smoke-filled room," otherwise known as a convention—not by Democratic voters.

When the voters pick, they tend to pick from the edges of their party rather than the center. That's what happened in GA-6 last year, a district that, on paper at least, appears much more competitive than PA-18. Trump only carried this suburban Atlanta district by two points—not 20. The Democrat, Jon Ossoff, and his allies spent more money on it than in any congressional race in history. And the GOP pick, Karen Handel, was an uninspiring candidate who had already lost some high-profile races.

Handel held on, in large part thanks to Ossoff, a pro-choice liberal who didn't live in the district. He gave Republican-leaning voters good reason to play it safe and stick with the GOP. Democrats lost a winnable seat.

Will the 2018 primary cycle bring the Democrats more Ossoffs, or Lambs? The PA-18 race is a signal to strong Democratic candidates thinking of running that this is a year they can win. But if they get beaten by more progressive, far-Left candidates in the primaries, they won't be able to help the Democrats' cause.

The big lesson of Tuesday night for Democrat is this: If you really want Nancy Pelosi to be speaker again, nominate more candidates who promise they won't vote for her.