Since the House expanded to 435 members in 1912, two-term presidents have actually lost more House seats in their first midterm (an average of 32 seats lost) than in their second (29 seats lost), according to a Fix review.
The six-year itch applies more to the Senate, with two-term presidents running about even in their first midterm and losing an average of five seats in their second midterm.
But even when talking about the Senate, it's much more common for a president to have one bad midterm. Over the past 100 years, only one president has had two really bad midterms (losing at least two Senate seats in both), and that's Harry Truman.
For every other president, if they had a bad first midterm, the second one wasn't as bad, and vice-versa. President Obama, of course, had a very bad first midterm, which suggests that the six-year itch isn't really in effect.
Only three of the last seven two-term presidents who were in office for both midterms had a bad second midterm in both chambers — George W. Bush, Dwight Eisenhower and Franklin Roosevelt.
Woodrow Wilson and Ronald Reagan both lost control of the Senate in their second midterms but actually performed better in the House the second time around.
None of this is to say that Obama has a good chance at his party winning back the House for the final two years of his term in 2014. In fact, over the past century, only one president's party has gained seats in the sixth year of his presidency — Clinton. (He only gained five seats in the House and the Senate stayed the same.)
And history suggests that Republicans could have a chance at winning back the Senate — something that has often happened in the sixth year of a presidency.
But the idea that there is something perilous about the sixth-year midterm, as opposed to the second-year midterm, isn't really borne out by the numbers — particularly in the House.
And if anything, the fact that Obama sustained huge losses in 2010 suggests his worst midterm is behind him, and the itch has been sufficiently scratched.