India, Oct. 24 -- There is a rule in American electoral politics so reliable, so durable, so resistant to the particularities of any given moment, that political scientists call it one of the closest things the United States has to an iron law: the president's party loses ground in midterm elections.

The president's party almost always loses ground in midterm House elections, as has happened in 20 of the past 22 midterm elections stretching back to 1938, and both exceptions reflected unusual circumstances.

On 3 November 2026, that law faces its most consequential test in a generation, in the most charged political environment since the Trump presidency's first term midterms in 2018, complicated by an eight-month war with Iran, inflation...