At the beginning of this year — back when the notion that Donald Trump might dominate the presidential race was a dystopian scenario as unimaginably remote as The Man in the High Castle — the most horrifying thing Republican insiders could imagine was a Ted Cruz nomination. In much the same way that Trump has set the terms of the presidential debate in ways that discomfited the party’s leadership and fired up the base, Cruz did the same in Washington. The intense loathing Cruz inspired among every professional Republican politician not named Ted Cruz made his nomination difficult to fathom....