Of the 18 midterms since 1950, there have been just five split decisions, where the House shifted towards one party and the Senate towards the other. And 2018's was the most split of them all.
Why it matters: Now that all of the races have been settled — with the exception of the California 21st district race — we can see how much of an outlier the 2018 midterms were. The split is also a sign of how Democrats dominated the suburban House districts while Republicans won the rural Senate states.
Between the lines: In modern midterm elections, the trend has been for seats in both the House and Senate to shift in one direction, usually against the president's party.
The strength of this year's blue wave depends upon how you measure it:
- If you measure it by Democratic seats gained in the House, or since Watergate, or by the margin of victory in the popular vote, it was the strongest Democratic wave since the 1974 midterm election.
- If you measure it by total seats gained by any party, the Republicans did better under Bill Clinton in 1994 and Barack Obama in 2010.
- And if you measure it by end results, 2006 was better for the Democrats — the year they won both the House and Senate under George W. Bush.
The bottom line: The split decision was no surprise, since the Senate map was historically bad for Democrats. That's why Republicans were able to survive and even improve their numbers a bit in the Senate. But it doesn't mean the wave wasn't there.