The same electorate that re-elected President Obama by more than 3 million votes and chose Democrats or Democratic-leaning Independents in 25 out of 33 Senate races also re-affirmed the Republican majority in the House 234-201. That’s not much different from the 242-193 advantage the Republicans got in 2010, which was considered a Republican wave election.

So how did that happen? Do voters “prefer divided government”, as Wisconsin columnist Tom Still concludes? Did they send a mixed message that gives a mandate to neither party’s agenda, as Paul Ryan claims? Or was a Democratic-leaning electorate thwarted in its will to have a Democratic Congress?

Consider this: More people voted for Democratic congressional candidates than Republican ones. As of November 9, the WaPo’s Dan Keating calculated the Democratic advantage at 48.8%-48.47%, or 49.55%-48.54% in races where both parties ran a candidate.

So how did the People vote (narrowly) for a Democratic Congress but get a Republican one instead? That’s certainly not what the Founders intended: The reason there are more House districts than Senate seats and all congressmen have to go back to the voters every two years is that the House is supposed to closely reflect the will of the People.

Why didn’t that work? Why didn’t the House come out with a slight edge for the Democrats, or something closer to a 50-50 split reflecting a close popular vote?

Gerrymandering.

Every ten years (after the census), the states redraw the boundaries of their congressional districts. 2010 was a census year, but it also was a year when Republicans swept the legislatures of several big swing states like Ohio and Florida, and even states like Wisconsin and Pennsylvania that ordinarily lean blue. So Republicans got to redraw the districts in those states to favor their own candidates.

There’s nothing illegal about that. It’s been going on forever. (The name comes from this 1812 cartoon, in which an oddly-shaped district is portrayed as Gov. Gerry’s salamander.) And both parties do it. (Though in recent years Republicans have been more aggressive about it, as when Texas redrew its districts without a new census in 2003.)

But it’s one thing to wave your hands and say “gerrymandering” and another to see how it actually works. The basic idea is simple: You load up a few districts with as many of your opponent’s voters as possible, leaving yourself smaller (but still comfortable) advantages in the other districts.

For example, suppose your state got 3 House seats and had 300,000 voters split equally between the Purple party and the Yellow party. If the Yellows control the state legislature, they can lock in a 2-1 House majority by drawing district boundaries that divide the voters like this:

District Yellow Purple 1 0 100,000 2 75,000 25,000 3 75,000 25,000 Total 150,000 150,000

That’s the ideal case, but now look at Wisconsin. Tom Still reports:

State voters sent a Democrat back to the White House, but maintained the Republican Party’s 5-3 edge in Wisconsin’s House delegation, very much in line with the national decision to keep the House in Republican hands, which will make Obama’s second term even tougher.

Look at the vote totals in those 8 districts. (Numbers retrieved from CNN on November 14.)

District Democrat Republican margin 1 157,721 199,715 41,994 R 2 264,790 124,465 140,325 D 3 217,328 121,536 95,792 D 4 234,823 80,637 154,186 D 5 117,972 249,267 131,295 R 6 136,146 223,514 87,368 R 7 157,340 201,318 43,978 R 8 156,371 198,464 42,093 R Total 1,442,491 1,398,916 43,575 D

So a Democratic advantage of over 40,000 votes, or 50.8%-49.2%, turns into a 5-3 Republican majority. It happens just like in the ideal Purple/Yellow example: All three Democratic wins are by at least 95,000 votes, but only one Republican victory is that big. Districts 1, 7, and 8 all provide comfortable 40,000-vote margins for the Republicans, but put together those margins don’t add up to the 140,000+ Democratic landslides in either District 2 or District 4. (BTW, District 1 is Paul Ryan’s seat.)

The bigger the state, the more room for this kind of mischief. A chart listing the 18 congressional districts of Pennsylvania would be too big to be instructive, but I’ve added up the numbers: Democrats got 2.72 million total votes compared to 2.65 million for the Republicans — yielding a 13-5 Republican advantage in House seats.