Just this week, three House Democrats announced they won't seek reelection in 2022: New Jersey's Albio Sires, Florida's Stephanie Murphy and California's Lucille Roybal-Allard. That makes 23 House Democrats who have announced they're retiring or running for another office next year, as the party braces for the possible loss of its already slim majority in the House in next year's midterm elections. 

By comparison, just 11 House Republicans have said they're not coming back after their 2020 term ends. Two members, Steve Stivers of Ohio and Devin Nunes of California, resigned before the end of their term to take new jobs elsewhere. 

It bears noting that just because a majority party has the greater number of vacant seats going into an election, it's not always the case that it will have a bad year.

For instance, there were 17 seats left open by House Democrats in 2010, compared to 20 on the Republican side, but the Republican Tea Party wave, an anti-tax, small-government movement, flipped the chamber and added 63 new GOP seats.