Going back to the election of 1862, the only time the president’s party gained as many as 10 seats was, well, never. Even in 1934, the best showing by the president’s party in House elections since the Civil War, the president’s party gained only nine seats.

In 1998, Democrats gained a handful of seats during Bill Clinton’s second midterm (five), and Republicans gained a somewhat larger handful during George W. Bush’s first midterm (eight). But in each case, unusual circumstances — post-impeachment fallout in 1996 and political fallout from the attacks of 9/11 (plus redistricting) in 2002 — help account for the atypical results.

So, while midterm elections have produced some huge swings well in excess of 17 seats recently — in 2010, 2006, 1994 and 1982, for example — all of those swings were in the favor of the party not holding the White House…

Midterm electorates tend to be whiter and older than presidential-year electorates, so turning out an electorate that looks more like 2012 (72 percent white, 19 percent 18- to 29-year-olds) than 2010 (78 percent white, 11 percent 18- to 29-year-olds) would help Democratic prospects.

But since the president will not be on the ballot next year, he will have to prove that his popularity can be transferred to other Democratic candidates or, more generally, to his party.