Donald Trump’s decision to make Sen. J.D. Vance (R-Ohio) his running mate is significant not just because he will be his ticket-balancing, ribbon-cutting sidekick, but also because the former president has sharply changed the direction of the party — and is now trying to consolidate it into its enduring future form. Given that Trump is 78, there is also an unusually high risk that Vance will actually end up sitting in the Oval Office sometime in the next four years. So I asked my colleagues...