Down-ballot races are increasingly decided by who wins the White House. To grasp this fact, it’s best to focus on two numbers: 6 percent and .781.
The first number is the total percentage of House districts that voted for different parties for president and for U.S. House in 2012. It was the lowest percentage in nearly a century. The second number is the correlation between the presidential results and the Senate race results in 2012. (Zero indicates no relationship, while one would indicate a perfect, exact relationship between two variables.) The correlation between presidential and Senate voting in 2012 was higher than it had been in more than half a century. MORE