If you had to bet right now, the odds are relatively good that Democrats will win back control of the House while Republicans retain the Senate (in fact, FiveThirtyEight considers each of those outcomes a four-in-five probability to occur) in the upcoming midterm election. And indeed, there’s a good chance Republicans will actually gain Senate seats even if they lose control of the House; that’s exactly what CNN’s Harry Enten projects.
How weird would that be? Well, not so weird at all if you look at the wildly pro-Republican Senate landscape this election year has produced, some of it attributable to significant Democratic over-performance in 2006 and 2012, which left them defending 26 of the 35 seats up this year, ten of them in states carried by Donald Trump two years ago. Yes, Democrats have made an impressive run, and could still pull out a Senate victory. But it’s never been a likely outcome.
It’s also worth knowing that historically, the two chambers of Congress moving in different directions is unusual, but hardly unprecedented. Each party has made gains in different chambers on six occasions since World War II. Three were in midterms (1962, 1970, and 1982) and three in presidential years (1960, 1972, and 1984). As you might expect from the nature of these two types of elections, the president’s party lost House seats and gained Senate seats in the three “split decision” midterms (House races are national in scope, making them more naturally a uniform reaction against the party controlling the White House), much as Republicans are likely to do on November 6. And given the greater likelihood of presidential coattails in presidential years (again, affecting the House most uniformly), it’s unsurprising that the party of the incumbent president gained House seats and lost Senate seats in the three “split decision” elections in presidential years.
There are some more specific precedents for 2018 as well. In 1970, when a Senate class built by Democratic landslides in 1958 and 1964 was up for reelection, Democrats found themselves defending a disproportionate 24 of 33 seats — an amazing 14 of them in states carried by Richard Nixon in 1968. They lost 3 net Senate seats while gaining 12 House seats. The landscape wasn’t quite so extreme in 1982; Democrats were defending 19 of 33 Senate seats. But 15 of them were in states carried by Ronald Reagan two years earlier. They lost one net Senate seat while winning 26 House seats.
One thing that has most definitely changed in recent years is a decline in ticket-splitting (at least in most states). It’s amazing to realize today that Republicans lost Senate seats in two of their biggest presidential landslide years ever: Richard Nixon’s in 1972 and Ronald Reagan’s in 1984. Some of that was due to the persistent strength of moderate-to-conservative southern Democrats who were not perceived as bearing the liberal sins of their national party. Thus in 1972 Democratic incumbent senators were reelected in Alabama, Arkansas, Georgia, Louisiana, and Mississippi even as Nixon carried their states by percentages ranging from 65 to 78 percent. Republicans lost two net Senate seats while gaining 12 House seats. There was a similar phenomenon in 1984 when Democratic Senate incumbents were reelected in southern states overwhelmingly carried by Reagan, and Democrats picked up a seat in Tennessee — as Al Gore won 60 percent even as Reagan carried the state with 58 percent. Republicans lost two net Senate seats as they gained 14 House seats.
But there have been mixed-result years when some more ideologically oriented ticket-splitting happened as well. In 1984, Iowa’s Tom Harkin beat an incumbent Republican senator by a landslide even as Reagan carried his state by eight points, leading to a 30-year period in which Iowa voters happily reelected the quite liberal Harkin and the very conservative Chuck Grassley, each by comfortable margins.
With ticket-splitting becoming more unusual, it’s taken a strange Senate landscape like 2018’s to produce the potential for such disparate results. It’s like flip-phones: once ubiquitous, now an oddity. Look now, because you may not see the likes of them again.
