Washington (CNN) It's easy -- and understandable -- to focus on whether or not Conor Lamb is going to wind up with more votes than Rick Saccone when all the ballots are counted from Tuesday's special election in Pennsylvania.

But the focus on the "W" sort of misses the point. And that point is this: This southwestern Pennsylvania district should have never been competitive -- or even close to competitive. This is not a swing district. It is not even a Republican-leaning district. It is, based on past presidential performance and congressional level results, a comfortably Republican seat.

And if comfortably Republican seats like Pennsylvania's 18th are competitive in this sort of national environment -- an unpopular president in the White House, Democratic base voters fired up over the prospect of sending Donald Trump a message -- then there are a whole lot of GOP members of Congress who need to start worrying this morning.

One way to measure -- and I think the best way to measure -- just how titanic Lamb's apparent victory is (and what it means for the fight for the House going forward) is to look at how many other seats Republicans currently hold that have similar or less GOP-friendly profiles than Pennsylvania's 18th.

Which brings me to the Cook Political Report's Partisan Voting Index or PVI . The goal of the PVI is to compare every congressional district to every other congressional district based on how it has performed in each of the last two presidential elections.

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