Largely because Donald Trump is so unpopular, his party will be trounced in the midterm elections in November. That is what The Economist ’s new forecasting model currently says. Democrats are almost certain to win the House of Representatives. They could even flip the Senate —a surprise for election nerds, because the map in this cycle strongly favours Republicans. Yet although the outlook for Democrats is good, for America’s democracy it is alarming.

Each party has come to see the other lot as cheats. Repeated meddling in election machinery by the president and his party, and their false claim that victory was stolen from them in 2020, have undermined voters’ belief that elections are fair. The degrading contest to gerrymander congressional seats, the most intense in memory, further tells Americans that their politicians want to rig outcomes rather than compete.

Some Democrats worry that Mr Trump will steal the midterms. That is unlikely. But you don’t have to expect the worst to fear the trend.…