If the new Dem president gets reelected and it's not a huge landslide, I would expect that Democrats don't pick up the House until the 2030 midterms.
No one president was able to win without SOME downballot succes since Nixon and he might be the only one.
Bush 41 did even worse than Nixon in that department. While Bush was winning in 1988, Republicans actually lost seats in both the House and Senate while starting from an already low base (only 178 House seats and 46 Senate seats).
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