If Trump doesn’t run, it’s not totally impossible. The GOP has changed over the past decade, but it’s not like a wholly different party. Historically, more moderate candidates have done well in GOP presidential primaries — Bush, McCain, Romney, to name a few. And even in 2016, Trump was seen as more moderate by primary voters than the alternative, Ted Cruz. So, who exactly knows up from down post-2016, but that’s some historical context to think about.
