Three of the worse Republican governors Sam Brownback, Bobby Jindal (now happily ex-governor), and Rick Snyder
Credit: AP/Reuters/Charlie Riedel/Brian Snyder/Rebecca Cook

Although Democrats have held the White House for eight years, during that same time they have suffered dramatic losses at the state level. Part of this is due to low turnout in midterm elections, which favors Republicans because low-income people, young people and people of color make up a smaller portion of the electorate. In addition, the out-of-power party tends to gain during midterm elections. A more recent development that similarly favors down-ticket Republicans is the power of big donors like the Koch brothers, who have poured hundreds of millions of dollars into elections to get conservative candidates elected at the state level.

Another theory is presented by Tyler Cowen, who argues, among other things, that:

At the state and local level, the governments controlled by Republicans tend to be better run, sometimes […]