US midterms: Senate

Although their elections are held on the same day, the United States Senate is quite a different beast electorally from the House of Representatives (see yesterday’s House preview here). Its members sit for six-year terms, with a third elected each time, so tomorrow there are only 34 seats to be decided,* compared to 435 for the House.

That means that it’s feasible to assess Senate prospects seat by seat in a way that it really isn’t for the House. And it’s also necessary to do it that way, because senators are much more high-profile and therefore have personal votes that can cut across national trends – not as much as they used to, but enough to make a difference.

The Senate is currently divided 50-50 between the two parties (counting the two independents with the Democrats), which gives the Democrats a bare majority since vice-president Kamala Harris has a casting vote. But there’s not much point in looking at the 2020 election; this crop of Senate seats were last voted on in 2016, which was a better Republican year. Twenty of the 34 are Republican-held, against only 14 Democrat.

That gives the Republicans a harder task than in the House, and it’s made worse by the fact that five Republican incumbents are retiring compared to just one Democrat. As a result, the Democrats started out confident of not just holding their majority but increasing it. Two months ago, FiveThirtyEight’s polls-only model gave them an 82% chance of holding control, with 52-48 being the most likely outcome.

But the reversal of fortune that we noted yesterday in connection with the House has happened with the Senate as well. The polls-only model still has the Democrats very slightly favored, with a 53% chance of control; the “Deluxe” model has flipped the other way, to just 46%. It is clearly much too close to call, but the majority of pundits seem now to be leaning towards the Republicans.

Of the 34, 24 can be regarded as safe: 15 Republican (Alabama, Alaska, Arkansas, Idaho, Indiana, Iowa, Kansas, Kentucky, Louisiana, Missouri, North Dakota, Oklahoma, South Carolina, South Dakota and Utah) and nine Democrat (California, Connecticut, Hawai’i, Illinois, Maryland, New York, Oregon, Vermont and Washington). If any of those come into contention, we can be confident that control of the Senate will not be at issue; a party losing one of those will already have lost comprehensively.

That leaves ten in some doubt. All of them are classic marginal states, closely contested by Joe Biden and Donald Trump two years ago. Trump won three of them – Florida, North Carolina and Ohio – and while those three all have Republican incumbents, Florida’s Marco Rubio is the only one seeking re-election. The Republicans are favorites in all three, but Rubio is the only one who looks reasonably secure.

The other seven states were won by Joe Biden. Five of them have Democrat incumbents (all seeking re-election): Arizona, Colorado, Georgia, Nevada and New Hampshire. Colorado’s Michael Bennet and New Hampshire’s Maggie Hassan are clear favorites, but the other three are on a knife-edge.

The two remaining states are Pennsylvania and Wisconsin: won by Biden, but among his four most marginal states (Arizona and Georgia are the other two) and having sitting Republican senators from 2016. Ron Johnson in Wisconsin is running again and appears to be in the lead. Pat Toomey in Pennsylvania is retiring, with Democrat John Fetterman and Republican Mehmet Oz neck-and-neck in the contest to replace him.

So the Democrats, despite what looked like a favorable position overall, now find that they have to win three of the four closest races – Arizona, Georgia, Nevada and Pennsylvania – to hold on to the Senate. And on election eve the betting market puts them behind in all of those except Arizona.

As I explained after the 2018 election, the Democrats have had a structural disadvantage in the Senate for some time, but it has become more acute in recent years with the growth of partisanship and straight-ticket voting. Demographic change has also widened the gap between large and small states, and plans to create additional Democrat-voting states have come to nothing.

The Democrats may just hang on tomorrow, but unless they can turn their electoral fortunes around they face a tougher task in 2024, when 21 of their senators (plus the two independents) will be up for re-election, including three that sit for Republican-voting states.

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* There are also two Senate by-elections, in California and Oklahoma, in addition to the regular elections in those states, but both seats are very safe (for Democrats and Republicans respectively).