A generous Senate map in last week's midterm elections helped Republicans keep a majority in the chamber even as they lost control of the House.
The GOP will not have such an easy path in 2020.
So far, Republicans have unseated three Democratic senators in this year's midterms, while Democrats have won two GOP-held Senate seats, according to projections. Depending on how a recount in Florida and runoff in Mississippi play out, Republicans could hold their current 51 seats or expand their majority to 53 seats in January. The election could have gone worse for Democrats: 26 Democratic senators and independents who caucus with them faced re-election this year, while only nine Republican-held seats were up for grabs.