We’ve seen presidential candidates in the past try to defend an unlikely choice of running mate. But we’ve never before seen a vice-presidential candidate try to defend a bizarre choice of nominee.

Yet that was the daunting task that Gov. Mike Pence of Indiana faced on Tuesday night, as he labored to defend Donald Trump, a nominee with contempt for many of the principles, much of the policy agenda and all of the dignity of the Republican Party that Mr. Pence cherishes.

Senator Tim Kaine of Virginia was on the attack from the start, declaring that “the thought of Donald Trump as commander in chief scares us to death.” Mr. Pence, cool and coherent where Mr. Trump, in his debate with Hillary Clinton last week, was petulant and erratic, made his own strategy clear right away: He set out to invent a new version of Donald Trump, one that he could believe in.

Mr. Pence simply ignored the Donald Trump we have seen on the trail for more than a year — the one who would build a wall against Mexico, the one who would disregard our security treaties and tear up our trade agreements, the one with a crush on Vladimir Putin — and instead dreamed up a more conventional, right-wing Republican, a Republican, that is, very like Mike Pence.