While we don’t know what the outcome of this year’s elections will be, history suggests that Johnson is likely to win and Republicans will not lose any of the seats they control to Democrats.
Why? Because the opposition party rarely loses Senate seats in midterms when those states had leaned toward them in previous presidential elections.
Since 1982, opposition-party incumbent senators from states like Wisconsin (i.e. lean toward the opposition party in the previous two presidential elections) have won 86 out of 87 elections in midterms.
Biden’s approval rating, right now, is mired at around 42% to 43% on average. It seems unlikely, at this point, that Biden will be popular enough for his party to overcome the traditional headwinds against the White House party this election cycle.
The chance that any of these Republican senators loses is small, if history is any guide. In fact, the correlation between the presidential lean of a state and how it votes in Senate elections has gotten stronger in recent years. In 2020, it was more than +0.9 (on a scale from -1 to +1).
(The growing correlation between how a party votes in Senate and presidential elections helps to explain why a number of Democratic incumbent senators lost in 2018. Although they were members of the opposition party with Republican Donald Trump as President, all the senators who lost were from states that leaned Republican on the presidential level.)
Democrats’ best chance to pick up a Republican-held seat is where Republicans are retiring. There are five of those seats, most notably in North Carolina, Ohio and Pennsylvania. All three voted more Republican than the nation in the last few presidential elections, but all have elected at least one Democrat to major statewide office in the last four years.
Still, even here, the math is not on the Democrats’ side. Since 1982, there have been 35 midterm Senate elections in states that leaned toward the opposition party in the previous presidential elections and where an elected incumbent was not an eligible candidate by the time of the election. The opposition party won 32 of the 35.
This year, the President doesn’t look like he’ll be popular. Nor do the Democrats have someone running for any of these seats who has anything close to the history that Manchin has of winning in a deeply red state.
Of course, maybe there will be some surprising results this year. History doesn’t always hold. But if it does, the Democrats’ chances of picking up seats in the Senate are small.