Why it's so hard for Democrats to win the House

Since the 2010 elections, Republican control of the House of Representatives has been the biggest obstacle for progressives trying to pass new laws. Democrats have longed to retake the chamber, and with historically low congressional approval and bad Republican favorability ratings, some now hope that their party's 2016 presidential nominee will be able sweep them back into control.

But it doesn't look likely that the GOP House will go away anytime soon. Democrats currently need to pick up 30 seats to retake the House, and there's little historical precedent for such a wave helping out the president's party. Indeed, no incumbent president's party has managed to achieve such gains since Lyndon Johnson's historic 1964 landslide.

And today's Democrats would have to pull that off while overcoming a set of built-in disadvantages for their party in House elections, including the geographic makeup of their coalition and the gerrymandering Republicans carried out in many states during the 2011-'12 redistricting.

If a Democrat wins the 2016 presidential election, the party could well make some gains in the House. But large wave elections unseating many House incumbents mainly tend to happen when the electorate is unhappy with the president about something. Otherwise — even when Congress is widely loathed, like it is today — voters tend to leave the vast majority of incumbents in place.

House Democrats face three built-in disadvantages

Back in the 2012 House elections, Democratic candidates won 1.4 million more votes than Republicans did. Yet when the dust settled, Republicans held a 234-201 majority in the chamber — well short of their current margin, but a clear majority nonetheless.

This dramatic discrepancy shows how difficult it is for Democrats to win the House even in a favorable year for the party. And it occurred for three main reasons:

1. Geography has a GOP bias: Many Democrats live close to each other in urban areas. Because they're naturally "packed" in, it's unnatural to draw a map dispersing those voters across many districts. Maps that favor Republicans are just easier to draw — geography has a built-in pro-GOP bias. Jowei Chen and Jonathan Rodden wrote that a map accurately reflecting the partisan split in most states is "unlikely to emerge by chance from a nonpartisan process." (Multi-member districts could fix this problem, except for the fact that Congress made them illegal.)
2. Incumbents usually win: In normal elections, most incumbents get reelected. The US had three historically unusual wave elections in a row between 2006 and 2010, where one party had an immense advantage over the other across the board and many incumbents were defeated — but even in those elections, the vast majority of incumbents were reelected. And 2012 was once again a fairly close election where most incumbents were returned to office. "On average, an incumbent in 2012 ran five percentage points ahead of a non-incumbent candidate from the same party in a similar seat," John Sides and Eric McGhee of the Monkey Cage wrote.
3. Partisan gerrymandering: When the GOP won control of many state legislatures during the 2010 elections, it got the upper hand in the once-a-decade redistricting process. In some states, they implemented some partisan gerrymanders that affected 2012 results. For instance, in Ohio, Pennsylvania, North Carolina, and Virginia, Republican candidates won between 49 and 53 percent of the House vote in each state, yet each state's congressional delegation ended up about 70 percent Republican. While analysts disagree on just how much of an advantage 2010's gerrymanders gave the GOP, there's general consensus that it's responsible for padding their majority by at least a few seats, and perhaps by many seats.

So it's clear that Democrats are unlikely to retake the House in any ordinary election year. What they would need is a nationwide wave in their favor.

House waves almost always hurt the president's party

The chart above shows how many House seats the incumbent president's party has either picked up or lost in recent decades. As you can see, losses are both far more common and far more dramatic than gains.

Again, Democrats currently need to pick up 30 seats to retake the House. The last time an incumbent president's party did that was 1964, when Lyndon B. Johnson won a 23-point victory over Barry Goldwater and Democrats romped nationwide to a 37-seat pickup.

An incumbent president's party has not come even close to that since. Richard Nixon and Ronald Reagan each won 49 states in their landslide reelections of 1972 and 1984, but they only picked up 13 and 16 seats in the House, respectively. And landslides like those are all but inconceivable today in our increasingly polarized politics. When presidential elections are closer, the makeup of the House tends not to change very much.

On the other hand, the party of the incumbent president frequently loses more than 30 seats. Democrats did so in 1966, 1980, 1994, and 2010, and Republicans did in 1974 and 2006.

So weirdly, the best shot for Democrats to retake the House probably involves a Republican being elected president. However, even then, that GOP president would have to become quite unpopular to foment a wave that would overcome all the Democrats' built-in disadvantages in House contests. Which means that even if House Republicans remain widely disliked, they'll still have a good chance to hold on to the chamber for years to come.

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