(* = by one arbitrary measure I just came up with)

After this year’s elections, the country could have fewer states with split partisan representation in the Senate since 1910. If my somewhat cursory research is correct.

Today, 14 of the 50 states have one Democratic and one Republican Senator. (I’m counting Independents Bernie Sanders and Angus King as Democrats, since they caucus that way.) The others each have two Senators from the same party: 16 have two Democrats, and 20 have two Republicans.

Fourteen split states is not unusual–at least, since the direct election of Senators began roughly 100 years ago.

However, that number was inflated by the extraordinary 2010 midterm elections, which saw Republicans win seats in usually blue-leaning states. Those states have, arguably, grown more blue in the past six years; plus, Democrats have a likely advantage because of turnout in a Presidential election.

The result: 11 of the 14 split states have a Senator up for re-election this year, including nine Republicans. Six of those Republican seats (Florida, Illinois, New Hampshire, Ohio, Pennsylvania, Wisconsin), and both Democratic ones (Colorado, Nevada), seem to stand a fair chance of flipping to the other party. In all of those cases, the state would no longer be split, but would have two Senators from the same party.

Of course, that could be countered by Senate seats flipping in other states–the states with two of the same party. But, only one seems like a close call at the moment: North Carolina, where incumbent Republican Richard Burr is considered more likely than not to win another term. Upsets are possible in Alaska, and Arizona, but those would indeed be upsets.

The bottom line: it’s fairly likely that the number of states with split Senate representation will drop to single digits–and possibly as low as six.

I did some scrolling through Senates, and I’m pretty sure the number hasn’t dropped below 10 since 1956–when, incidentally, there were two fewer states. (Alaska and Hawaii were admitted in 1959.) And that was just a brief stint at nine, in between Oregon Independent Wayne Morse’s decision to caucus with the Democrats in 1955, and the election of Kentucky Republican John Sherman Cooper in late 1956, to fill the vacancy caused by Democrat  Alben Barkley’s death. (The more you know!)

The number might have briefly dipped to nine at some point earlier in the 1950s; it doesn’t look like it to me, but I can’t say I gave it a real scholarly level of review or anything.

And before that, you have to go back, I believe, to the 61st Congress, which met in 1909 and 1910. There were only 46 states; the state legislatures appointed Senators, and the country was still pretty cleanly split between the solid Democratic South, and the solid Republican everywhere-else. Only six states–Colorado, Indiana, Kentucky, Missouri, Nevada, and Oregon–had split Senate representation.

And here’s the kicker: the number could actually get even lower after the 2018 elections.

Obviously a lot could change, but right now the six seats that look most likely to flip parties in 2018 are all in split states–mostly products of Democrats winning red state seats in 2012, that will be hard to defend in a mid-term election. Those include Indiana, Missouri, Montana, North Dakota, and West Virginia; Nevada’s Republican-held seat is the other question mark.

All of this is to say that we might–might–be on the cusp of moving to an essentially unprecedented divide between solid-red and solid-blue states, in Senate representation.