Some people warned President Obama would lose in 2012 because no president since FDR had ever been reelected with an unemployment rate above 7.4 percent. The problem was that there had only been nine presidents who ran for reelection since FDR. That's just not a very big sample size. Obama proved those predictions wrong, winning with a 7.9 percent unemployment rate. The conventional wisdom going into the 2014 midterm elections is that Democrats are toast, because since 1938, the president's party has always lost a ton of seats on Congress in the sixth year of his presidency. But because not every presidency has had a sixth year, that's an even smaller sample size — seven sixth-year midterms since 1938, and that's if you count Lyndon Johnson, who was really only in his third year as president.

If the 2014 election were held today, 41 percent of voters would vote for a Democrat for Congress, while 37 percent would vote for a Republican, according to Quinnipiac University poll released Wednesday. This "would violate the historical model of the president's party losing ground in the sixth year of a presidency," the pollster says. But Real Clear Politics' Sean Trende says the "six-year itch" is actually a myth.

For one thing, just as with the old Unemployment Rule, "the only reason for using 1938 seems to be that the rule simply doesn’t hold up all that well if you go farther back," Trende writes. (No president since FDR had won with a high unemployment rate, they said, because FDR won with a high unemployment rate.) The Six Year Rule is based on a small number of elections, and analysts make excuses for 1986 and 1998, when the president's party didn't do so bad. If you expand the number of elections covered back to the Civil War, as in Trende's chart at right, the sixth year doesn't look quite so treacherous.

More important, if you look at both midterms elections for two-term presidents, the pattern is more clear: "Two-term presidents almost always get thumped in one midterm election, but they almost never get thumped twice."

RCP's Trende says there are a few reasons for this — the business cycle means that odds are that there will be an economic downturn at some point in a two-term administration. And when presidents are elected to their first term, they have stronger coattails, which means people from their party get elected in states where that party is not so popular.

If you look at especially bad midterms for presidents, you notice those were often moments that presidents' policies became very unpopular. The 1974 midterms, which were bad for Republicans, came right after Richard Nixon resigned. The 2006 midterms were horrible for George W. Bush, after the Iraq war had become unpopular and he struggled to respond to Hurricane Katrina.

A massively unpopular policy could theoretically cost Democrats a lot of seats. It could be the implementation of Obamacare, The Hill's Elise Viebeck reports. An anonymous Democratic lawmaker said he's worried Obama isn't selling the policy well enough:

“While you’re lining up the operational elements, you’ve got to start to reach out and communicate … I’ve said [to senior officials], ‘You guys need to pivot, quickly, from the wholesale to the retail, or you need to do both at the same time.’” 

Democrats lost a ton of seats in 2010, meaning there are fewer vulnerable Democrats in the House. If they're less likely to be slaughtered in the midterms, what are the chances they'll win the 17 seats needed to win back the House? Republicans plan on using Obamacare in the midterms, but Democrats think they have better chances in red states, because Obama won't be on the ballot.