Here’s a striking fact from Dave Wasserman, a specialist on US House of Representatives races for the Cook Political Report:
What if D's won every place w/ electorate less than 75% white, lost everywhere else? D's would win 292 EV's but just 36 Sen/191 House seats.— Dave Wasserman (@Redistrict) July 23, 2016
Now this is obviously a bit of an oversimplification. Democrats due very well in Vermont, which is extremely white, and they win more often than they lose in New Hampshire and Maine, which are even whiter. Then, on the flip side, the Deep South states of South Carolina, Georgia, Mississippi, Alabama, and Louisiana all fall below Wasserman’s 75 percent threshold while remaining reliably conservative.
But an oversimplification is sometimes useful in drawing out an underlying principle. And that’s what we see here. The political geography of the United States is such that the electorate for the median House seat and the electorate for the median Senate seat are both much whiter than the nation as a whole. This means that to win governing majorities, Democrats probably need to recruit and support a substantial cohort of legislators who are meaningfully less liberal than their presidential nominee.
Because moderate Democrats are much less conservative than mainstream Republicans, recruiting such candidates would move politics to the left overall. Still, it often “feels” wrong to say that shifting the Democratic Party to the right is the correct solution to frustrations with presidents’ lack of achievements.
Republicans, by contrast, probably get the better side of this deal. Their presidential nominees will lose more often than they win, but because it’s just one office they’ll still win sometimes due to fluky events (recessions or terrorist attacks or email server controversies or what have you) and when they do win they’ll have Congress at their back to push a robust agenda.