Democrat Conor Lamb's near-certain win in a western Pennsylvania district President Trump carried by 20 points brings his party one seat closer to the 24 they need to pick up for a majority, but it's another broad sign of danger for House Republicans.

At this writing, Lamb holds a 627 vote lead over Republican Rick Saccone with all precincts and absentee votes counted. Although a handful of provisional and military ballots remain and Saccone can technically request a recount, it's extremely unlikely those would change the result.

According to the Cook Political Report's Partisan Voter Index, there are 118 Republican-held districts less friendly to the GOP than PA's 18th CD (R+11), including 17 where the GOP incumbent isn't running in the fall and an additional vacancy in Ohio's 12th CD that will be settled by an August 7 special election that could become problematic for Republicans.

Are all of these 118 seats suddenly in play for Democrats? Of course not. Most feature well-funded GOP incumbents who are well aware of political headwinds and won't get outspent as badly as Saccone was. In addition, very few of them have the kind of Democratic DNA (a lingering voter registration advantage) that was on display yesterday, as Lamb restored his party's old strength in union bastions that had voted Trump.

More importantly, most won't feature Democratic nominees who are as perfect fits for their districts as Lamb was. Democrats couldn't have dreamed up a better candidate than a young, Catholic prosecutor and Marine who didn't have a political record to attack and broke with his party's prevailing positions on new gun restrictions, energy and tariffs. But, many Democrats with similar profiles are running in dozens of GOP-held seats, and Democrats only need two dozen seats to win control.

House Democrats deserve credit for largely staying off the Pittsburgh airwaves, a departure from past special election losses. This allowed Lamb to run his own race and credibly make the case he wasn't beholden to either party. Meanwhile, Republican outside groups tried out a variety of messages on Nancy Pelosi, tax cuts and Lamb's prosecutorial record. None of the lines of the attack moved the needle enough for the responsible groups to stick with them for long.

Over the course of the last year, there have been seven special elections for Congress. Including Alabama's Senate race, Democrats have overperformed their "typical" share of the vote (as predicted by Cook PVI) by an average of nine points. Excluding Alabama, Democrats have overperformed by an average of eight points, indicating a clear pro-Democratic enthusiasm gap and strong potential for a November wave.

A Smarter Way to Interpret Special Elections

The Pennsylvania outcome will reverberate nationally and locally. Nationally, Republicans will need to work to avoid more retirements. Filing deadlines have passed in only a handful of major states, including California, Illinois, Ohio and Texas. They'll also need to research and test for effective lines of attack against potential Democratic nominees.

Locally, the most pressing question is who will file to run where in November, as the filing deadline is next Tuesday and candidates must gather 1,000 valid signatures to appear on the fall ballot. Pennsylvania's fall elections will be held under all-new lines (per the recent court decision) that give Democrats up to 5 additional pickup opportunities.

Lamb is all but certain to run in the new 17th CD, a seat that's almost tailor-made for him. It includes his suburban Allegheny County base and is eight points less Republican than the 18th CD he appears to have just won. GOP Rep. Keith Rothfus lives there too and is likely to file there, but Lamb would start out as the favorite. Meanwhile, Saccone has signaled his intention to run in the 14th CD to the south, which is three points more Republican than the current 18th CD.

We'll have a complete rundown with ratings for the new districts in next week's report after the filing deadline passes.