President Obama is going to become more personally involved in the effort to retake the House of Representatives for Democrats in 2014 than he was this past election, Roll Call reports. For his effort to be successful, he’d have to make history.

There’s a phenomenon in American politics known as the “six-year” itch, which is the tendency of voters to reject a two-term president’s party in his sixth year in office. There are a number of explanations for this — scandal, disillusionment of the president’s base, hunger among the opposition. But for whatever the reasons, there has never been a case since the Civil War (i.e since the Democratic and Republican parties co-existed) in which a president regained control of the House for his party in the sixth year of his presidency.

As the table below shows, since the Civil War, there have been seven presidents who served at least two consecutive full terms. (Thus, this table leaves out Teddy Roosevelt, who took over after William McKinley’s assassination in 1901 but never served a full eight years, or Richard Nixon, who resigned in 1974).

In five of the cases, the president’s party lost at least 20 seats and as many as 96. In only one case — Bill Clinton in 1998 — did the president’s party gain seats. But even then, the gain was only a modest five seats and it wasn’t enough for Democrats to retake the majority. For Democrats to gain control of the House of Representatives in 2014, they would have to pick up a net of 17 seats.

Liberal Kevin Drum at Mother Jones has argued that 2014 might break this trend. But I think it’s likely to hold, for several reasons. One, the redrawn Congressional maps are likely to protect Republicans at least until the second half of the decade. Two, the composition of the electorate in midterm elections is likely to be much more favorable to Republicans than the electorate Obama was able to galvanize during a presidential election year. Three, Obamacare’s major provisions will be implemented in 2014 and I’m betting against it going smoothly. This isn’t saying it can’t be done — seven such elections  is a pretty small sample size and Republicans aren’t exactly popular right now. But it’s still unlikely.