Taking a Spin: A Democratic Victory With Limits

In this week's spin of Leo's Senate wheels, we get a forecast in which Democrats have an excellent election night. They hold the Senate by winning every competitive, Democratic-held Senate seat except Louisiana, while pulling off an upset in Montana.

Such a strong showing - controlling 52 seats - would probably require a shift in the national political climate toward Democrats, but perhaps not a huge one. Even 2012-like conditions, in which the president's approval rating is around 50 percent and Democrats have an edge on the generic ballot, could be enough. It would need to be coupled with some combination of strong Democratic and weak Republican campaigns in states like Alaska, Montana, Arkansas and North Carolina.

But at the same time, Senator Mary Landrieu loses re-election in Louisiana, and Democrats fail to win two Republican-held seats: in Georgia, where Michelle Nunn, the Democratic nominee, faces David Perdue or Jack Kingston; and in Kentucky, where Mitch McConnell, the Republican Senate minority leader, duels Alison Lundergan Grimes.

It's possible to imagine Democrats doing so well nationally while losing those three states, which pose particular challenges for them. In all three states - along with North Carolina - there's a case that the Democrats could run a flawless campaign and still lose. There are serious questions about the viability of the Democratic candidates' pathway to 50 percent of the vote. In Georgia and Louisiana, it's mainly because of demographics and racial polarization. In Kentucky, Ms. Grimes will have to win without huge Democratic margins in coal country - traditionally an essential part of the Democratic route to victory.

These challenges are less acute in states like Alaska or Montana, where there are larger numbers of swing voters.

The point is not that Democrats cannot make it to 50 percent in these three states, merely that the limits of the Democratic coalition there raise the possibility that they cannot. And in this scenario, even a strong Democratic year would not be enough to lift Ms. Landrieu, Ms. Grimes and Ms. Nunn over the top.