But declining approval ratings may be a warning sign for endangered Republican incumbents in battleground states. The partisan lean metric in the table above measures how much more Democratic- or Republican-leaning a state is than the country as a whole,3 and 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).

This is particularly worrisome for Sens. Susan Collins of Maine and Cory Gardner of Colorado, who will likely need some ticket-splitting in their Democratic-leaning states to win reelection. Most notably, Iowa Sen. Joni Ernst’s net approval rating dropped about 9 percentage points, falling into negative territory, though it dropped the most among Republican voters, who may come back into her fold by Election Day. Democrats probably need to defeat most or all of these senators — North Carolina Sen. Thom Tillis is the fifth — to capture the Senate, and they have to be pleased that the public image of these incumbents has taken a hit. Of the Democrats 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).