Dave Wasserman of Cook Political Report currently lists 55 House Seats as “competitive” (tossup or lean Democrat or Republican). Of those 55 seats, 50 are currently held by the Republicans and 5 by the Democrats. The Republicans currently hold control of the House by a 23 seat margin, meaning Democrats would need to win 27 of those 55 seats to flip control.
https://cookpolitical.com/analysis/h...s-13-districts
The link below lists the 55 seats that will likely decide control, plus the next level of seats that are “likely” Democrat or Republican, but not considered totally safe.
https://cookpolitical.com/ratings/house-race-ratings
If you look at the seats in question, it’s Republican congressmen in districts won by Clinton in 2016, or those holding seats in suburban districts that are the most vulnerable. Four of the 5 D seats are open, with 2 in Minnesota.