The cliché is true: This is the most important U.S. midterm, ever

Non-Trump Republicans such as Jeff Flake and Paul Ryan will continue to quit. They will be replaced by Trumpish National Front-style politicians. Trump himself will double-down on the racial and “deep state” themes that seem to be rewarding him so richly. And Trump voters will feel liberated from “political correctness” to be more openly racially provocative in public, as in Charlottesville last year.

At the moment, it is still possible to argue that Trump is an “accidental president”. He lost the popular vote, apparently did not want to win, does not take the job seriously, and does not seem to have much of a policy agenda beyond his grievances – “owning the libs,” attacking anything Obama did, feathering the nest of the Trump conglomerate.

But a victory in the midterms would end this option for dismissing Trump. If 2018 and 2020 do not deliver a sharp rebuke to the GOP – not just Trump, but the GOP in general – the Trumpist turn will continue. The GOP will become even more extreme than it is now, especially on race and constitutional norms of fair play.

As asymmetric polarisation worsens, the country will become increasingly ungovernable.