At FiveThirtyEight, Geoffrey Skelley writes:
“Republicans are favored to hold on to the Senate, as they currently have a 53-to-47 seat edge, which means Democrats must gain a net of four seats for outright control, or three seats and the vice presidency, as the vice president casts the tiebreaking vote. What’s more, the competitive races in the Senate in 2020 will probably be on Republican-leaning turf, which should give the GOP a baseline advantage. However, Democrats’ silver lining is that the GOP has to defend 23 of the 35 seats on the ballot next year, and election forecasters Inside Elections, Sabato’s Crystal Ball and The Cook Political Report currently rate Democrats’ opportunities to pick up seats more favorably than Republicans’. (Though Republicans, of course, can win the Senate by simply hanging on to the seats they have.)
And keep in mind that the presidential race at the top of the ticket may be critical in determining which party wins control because of just how nationalized our elections have become. In the 2016 election, for instance, every state with a Senate race backed the same party for both president and Senate for the first time ever.
Skelley provides a chart showing the current “partisan lean” of every 2020 U.S. Senate race, and notes that “all five GOP senators defending seats in states with a partisan lean of less than R+10 saw their approval ratings worsen in the third quarter of 2019, according to data from Morning Consult. And all but one — Arizona Sen. Martha McSally — has a net negative rating (approval rating minus disapproval rating).”
At this political moment, polls indicate that the most vulnerable Republican Senators include Tillis (NC) and Ernst (IA), in addition to McSally. Skelley rates the Gardner (CO) and Collins (ME) races in toss-up territory. Plus there is an open seat in GA, where Dems may benefit from favorable demographic trends since 2016.
As for Democratic seats, Skelley notes that “in currently competitive contests (that is, those not rated as “safe” for either party), only Minnesota Sen. Tina Smith saw a decline in her net approval, although it remains fairly positive overall (+13).” Doug Jones (MS) has the toughest race, followed by Democratic Sen. Gary Peters (MI). Dems may need a landslide presidential win to regain a majority of the U.S. Senate.
Absent that landslide, Dems have a pretty narrow path to regaining a Senate majority. Sure it could happen, with some strong candidates. But Dems may profit more from studying how gubernatorial candidates Stacy Abrams and Andrew Gillum nearly won their 2018 statewide races in GA and FL respectively.