Earlier this year, we looked back at the seats that the ‘out-party’ was able to flip in the last three midterm elections.

Not surprisingly, we found that the easiest seats for the other party to flip are those the incumbent party holds, but the opposite party’s presidential nominee carried in the previous election. In 2010, for example, Republicans won 75 percent of the Democratic-held CDs that John McCain had carried in the 2008 presidential race. In 2018, Democrats won almost every one of the 26 districts held by a Republican that Hillary Clinton had carried in 2016.

We also found that the larger the margin of victory for an incumbent president in a district, the less likely that district is to flip, even in so-called “wave” elections. For example, in 2018 Democrats won just about every CD that Donald Trump won by 5 points or less (82 percent), they won just 23 percent of the districts Trump carried by 6-10 points. Few congressional districts the president won handily in the previous election have flipped. In 2010, a year

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