There weren’t too many of these split-ticket voters (Biden outran Ossoff by only 1.6 percentage points statewide), but as you can see in the map below, we have a sense of where Ossoff and Warnock need to make up ground: Suburban or well-educated areas, such as the Atlanta metropolitan area, including Fulton (where Biden did 2.8 points better than Ossoff), Cobb (2.4 points better) and Forsyth (2.1 points better) counties. (It’s easiest to use Ossoff’s vote share as the comparison point because multiple Democratic candidates were on the ballot in the other Senate race, so Warnock advanced to the runoff with less than 33 percent of the vote. However, the numbers are still similar when you compare Biden with the total Democratic vote share in the special election.)

The greater Atlanta area was not the only spot where Biden outperformed Ossoff, though. He also did so in well-educated Clarke and Oconee counties to the east — perhaps owing to the University of Georgia’s presence there. (The pattern also shows up in a handful of rural counties, such as Early County in the southwest, but this is probably less important. These counties are so small that just a few Biden-but-not-Ossoff voters can produce what looks like a big swing. So the most efficient strategy for Ossoff and Warnock is probably to focus on squeezing more votes out of metro Atlanta. The top six counties where Biden outperformed Ossoff the most in terms of raw votes were all located there.)