Why is the American midterm election this November such a big deal, and what does Trump mean by 'it's all about 35 races'?

Midterms decide who controls Congress, and Congress decides whether a president can pass laws, get budgets through, or face serious investigations. With Republicans holding both chambers by narrow margins, and the president's approval numbers sagging under an unpopular war and voter unease about the economy, control of the House in particular is up for grabs.

Trump's '35 races' comment, made at a Rose Garden dinner for vulnerable Republicans this week, is actually a fairly accurate description of how the House works. Most of the 435 seats are safe for one party or the other. The outcome comes down to a few dozen competitive districts, and that is where he says he will campaign in the final thirty days. His argument to those lawmakers was that they should run on his record rather than distance themselves from him.

The strain is visible. Some battleground Republicans decline to say whether they want him campaigning in their districts. A midterm convention in Dallas next week, billed as a celebration of the president, has a lot of candidates quietly finding other commitments.

There are also legal fights with real consequences: the administration is asking the Supreme Court to let a new Postal Service rule on mail-in ballots take effect, and the Missouri Supreme Court just threw out a Republican-drawn congressional map. Those rulings could shift a handful of seats, which in a 35-race election is everything.