If something goes wrong, you own it: Did the economy tank under George W. Bush? Yes. Was his decision to go into Iraq disastrously wrong? Yes. Does it matter this November? No. Iraq and the economy were two huge reasons why Obama won the 2008 nomination and then the general election. But after six years, there’s no strength left to the “it-was-the-last guy’s fault” argument. (The memory of Herbert Hoover helped FDR’s Democrats gain seats in the 1934 mid-terms, but by Roosevelt’s sixth year, the economic contraction cost his party big midterm losses.) If the Taliban’s gaining strength in Afghanistan, and if murderous extremists control large swaths of Iraq, the public knows the buck stops with Obama.

Your strengths matter less: In the fall of 1986, Ronald Reagan was still a popular president, with a Gallup job approval rating of 63 percent, as the arms-for-hostages-Iran-contra story didn’t break until just after the midterms. That’s one reason why Republicans only lost five House seats that fall—a fine showing for a six-year midterm. The Senate was a very different story. Six years earlier (which turned out to be the last time a Presidential candidate had real coattails) Reagan had helped elect 12 new Republican Senators. But with no Gipper on the ballot, seven GOP incumbents lost their seats,(many by very close margins) in states like Alabama, Georgia, Florida, North Carolina, North and South Dakota—all places where Reagan had won huge margins just two years earlier.

By contrast, Obama’s job approval numbers are underwater. But his absence from the ticket will still hurt Democratic Senate candidates in states like Michigan, Colorado, and North Carolina, where aggressive efforts helped turn out large numbers of blacks and Hispanics in his two Presidential runs.