The US Senate is so much a matter of local and personal factors that it’s hard to generalise about. But the House of Representatives is a bit more like the sort of nationwide election that Australians are used to.
At the last election, in 2004, the Republicans won 232 of the 435 seats, on a two-party vote of about 51.3% – there is no preferential voting, so votes cast for minor parties have no effect on the result.
To gain the 15 needed for a majority, the Democrats needed a uniform swing of 5.2%. (The boundaries have a slight bias towards the Republicans, since most of them were drawn by Republican legislatures.)
They did a bit better than that. A few seats are still doubtful, but it looks like a total gain of either 28 or 29 seats (the uncertain one is Connecticut’s 2nd district, where the Democrat challenger leads by just 170 votes).
Aggregate votes haven’t been tallied yet, but the two-party swing seems to be between 6 and 7%. A 7% uniform swing would have delivered 26 seats.
Because incumbents are so powerful, swings are even less uniform than in Australia. Five of the six most marginal Republicans are holding on; the gains are disproportionately in seats where incumbents had retired or fallen victim to major scandals. Mark Foley’s seat, for example, recorded a 13% swing.
Nonetheless, the total swing is still a good guide: deviations from uniformity may be greater, but they do roughly cancel out.
The geographical distribution of the changes is also interesting. Of the 29 likely Democrat gains, 11 are in the north and eight in the midwest. Only 10 are in the south and west, where most of the country’s population lives, and only three of those – two in Florida and one in Texas – are in the deep south.
For most of the twentieth century, Democrat majorities in congress rested on solid control of the south and a minority, but competitive, position in the rest of the country.
Over the last 40 years the Republicans have pursued a “southern strategy”, completely reversing the position in the south, which with a few exceptions is now solidly Republican.
What has changed in this election is that the Republicans are looking less than competitive in the north and midwest. Voters who used to vote for moderate Republicans such as Rhode Island’s senator Lincoln Chafee have become exasperated with the southern-based hard right and are switching to the Democrats.
Only time will tell whether that will induce the GOP to change tack, or just further cement extremist control.