Try this setup instead: It’s 2017. After Mr. Trump’s landslide defeat, President Clinton has a Democratic Senate and House of Representatives. The Republican National Committee has just released its latest post-mortem — it probably looks a lot like the post-2012 soul-searching exercise, the Growth and Opportunity Project, which encouraged moderation in tone and inclusiveness in policy.

But that blueprint is ignored. Instead, the party quickly regroups in opposition to the incoming administration. Most Republican voters hate Mrs. Clinton even more than they hated Mr. Obama. The conservative apparatus for sowing discontent with a new administration is in place, flush with cash and battle-tested.

For Republicans in and outside government, it will be a time not for facing up to hard truths but for doubling down on hardball tactics.

American voters choose presidents, not kings (or queens). American political institutions are, and were designed to be, a complex system of interlocking parts. The drama of presidential campaigns should not blind us to these longstanding and deeply rooted dynamics or to their perverse effect: They allow the Republican Party to thrive even as its presidential candidates do not.