Both chambers of America’s Congress may flip in November

Americans will elect 471 federal officials in November: 435 members of the House of Representatives, 34 senators, a vice-president and a president. These contests are overshadowed by the impending rematch between President Joe Biden and Donald Trump, his predecessor, which will be pitched as a struggle between democracy and autocracy (and amplified by a projected $3bn in campaign spending). Seven months of this promises to be wearing.

Cast your eye down the ballot, however, and something exotic is in the offing. At the moment, Washington is divided by the thinnest of margins. Democrats control the Senate by just two seats out of 100. Republicans control the House of Representatives by five out of 435 (a margin that will shrink to four once Mike Gallagher of Wisconsin retires next month).

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After the election, control of both chambers could flip. In the Senate, the seats contested this year are in extremely favourable states for Republicans. In the House, by contrast, Democrats campaigning against the chaos of Republican leadership may wrest back control. A double flip would be quite a feat of political gymnastics: it has never happened before.

Senate terms last six years, and only one-third are contested every two years. The mix this year is unkind to Democrats. Joe Manchin, the West Virginia senator who managed to remain the Democratic representative of his Trump-loving state, is retiring. His seat will almost certainly be filled by a Republican, leaving the starting-point for the race at, in essence, 50-50.

Of the seven competitive Senate races this cycle, all are now