American democracy is weird! If things go very sideways in the Electoral College, the election of the President may be thrown to the House. Under the procedure set forth in the 12th Amendment, the House votes by delegation: Each State gets a single vote.
Right now, Democrats control 24 delegations. Republicans control 25. Pennsylvania is split down the middle. Importantly, though: If the 2020 election is decided by the Twelfth Amendment process, the new House, the one elected in November, is the one that picks the President. It's not too late to improve those numbers!
Here, then, are the House races that will have the greatest impact on whether Donald Trump can be re-elected by the House in the unlikely event of a catastrophic Electoral College meltdown (including a meltdown instigated by lawfare or chicanery in the Senate-run Electoral Count process). These are all battleground/contested races where Democrats either need to pick up or hold a single seat in order to gain or maintain control of a delegation. Just a few flips here could make the difference.
PA-01 (pickup) (Eugene DePasquale)
PA-10 (pickup) (Christina Finello)
FL-15 (pickup) (Alan Cohn)
FL-27 (hold) (Debbie Mucarsel-Powell
AK-AL (pickup) (Alyse Galvin)
MT-AL (pickup) (Kathleen Williams)
MI-03 (hold, sorta) (Hillary Scholten)
MN-01 (pickup) (Dan Feehan)
MN-07 (hold) (Colin Peterson)
IA-2 (hold) (Rita Hart)