House Math and History

Just about every election analyst and handicapper agrees that the House is all-but-certain to flip. The only disagreement these days is how many seats Republicans will gain. 

On paper, the grim political environment suggests the kind of wave election that rivals the wipeouts of 1994 and 2010, when the party in power lost more than 50 seats. 

However, our current forecast, as analyzed by House editor David Wasserman, is for GOP gains in the 20-35 seat range. 

Why don’t we foresee 50-60 seat sweep? 

As my colleague Charlie Cook wrote recently, “big wave elections have tended to come from a party well behind in seats. Republicans’ House gain of 54 seats in 1994 was from a starting point of just 174 seats; their 64-seat pickup in 2010 was from 178 seats. When Democrats gained 42 seats from Republicans in 2018, they started with just 194 seats. Allocating the currently vacant seats into the column they had come from (and will likely return), Democrats hold 222 seats and Republicans 213, well above the GOP levels going into 1994 and 2010 and Democrats in 2006.” In fact, Charlie writes, a gain of 34 seats would equal the highest number of seats held by Republicans since the 1928 election.

Let’s first look at the kind of districts the party in power lost in the last three midterm elections.

The first thing you notice is 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. 

Not surprisingly, the larger the margin of victory for the incumbent president in a CD, the less likely that district is to flip. For example, while Democrats won just about every CD that Donald Trump won by 5 points or less in 2016 (82 percent), they won just 23 percent of the districts Trump carried by 6-10 points. Very few congressional districts the president won handily in the previous election have flipped. In 2010, a year in which Republicans netted 64 seats, only 15 percent of those seats (10) came from CD’s that Barack Obama had won by 10 points or more. 

In other words, even in big “wave” years, it’s hard to flip districts that are deeply red or deeply blue. In the last three midterm elections, a majority of the seats gained by the party not holding the White House (anywhere from 56 percent to 74 percent), came from districts that either the president carried by less than five points or had lost in the previous election. 

So, let’s look at the current map and assume both a high-end and low-end scenario based on these past election results. For example, 2018 was the high-water mark for the percentage of districts flipped that the president carried by five points or less (82 percent). The lowest in this category: 30 percent (2014). 

Under the high-end scenario, the GOP would gain 41 seats. The lower-end scenario shows Republicans picking up 19 seats. Remember, this is not the net, as we haven’t factored in GOP seats that may flip to Democrats. Right now, we list 10 GOP-held seats as vulnerable.

Bottom line: if Republicans are going to pick up the 50-60 seats they did in 1994 or 2010, they are going to need to win a significantly higher percentage of districts that Biden carried by more than 10 points. In the ‘old days’, many of the incumbents in those ‘safe seats’ would scoff at any suggestion that they could be in danger. But, after four straight wave elections, most of those members have (or at least should have) learned to take these warnings seriously.

Cook Political Report Research Associate Matthew Klein and intern Peter Jones contributed to this report.