Trump’s campaign to discredit the GOP would benefit from any attempts, whatever their motivations or consequences, to rewrite convention rules now, in the middle of a process that all participants began on the assumption that this year’s rules were settled. Next year, however, when this year’s competition is, like Trump, just a fragrant memory, state parties that have open primaries should rethink this practice. It makes parties susceptible to free-floating voters and freebooting candidates who are, like Trump, lightly — if at all — invested in the party’s historic mission and its future. Open primaries are not unconstitutional but they are discordant with a First Amendment value — the freedom of the individual to associate with like-minded persons in political parties to advance a particular political doctrine.

Reformers are apt to revive familiar proposals for making the nomination process tidier by instituting four or five rotating (in their places on the nominating calendar) regional primaries. Leave aside the question of whether tidiness, an essentially aesthetic value, is a sensible political goal for a complex continental nation. But this arrangement, which this year might have quickly nominated Trump, or any future reform must be evaluated in terms of how it would facilitate or impede future Trumps. Measures to prevent candidacies like his could be his contribution — inadvertent, of course — to the public good.