Score one for competence — and for Gov. Mike Pence — but the Republican running mate’s performance in Tuesday night’s vice presidential debate also underscored how ill-suited Donald Trump is for the presidency.

First, Pence was in command of his substance, his message, his delivery and his temper. He politely pointed out when Democratic candidate Tim Kaine was being rude — which was often — and counterpunched with the self-control that Hillary Clinton showed in last week’s presidential debate. He steadfastly refused to be drawn into the trenches of fights over Trump’s outlandish behavior. In that way, too, he debated in a manner that — if more dry — was reminiscent of Clinton.

If Republicans are looking for a candidate of the future who can competently articulate the GOP’s view of the world, they could do much worse than Pence. Surely, many Republicans and some Democrats wondered if a dry, but stable, GOP nominee like Pence would be taking better advantage than Trump of the political atmospherics — the populist anger of the moment and the traditional inclination to switch parties in the White House after a two-term run.

On that level, Pence did himself and his party a great service. Without ever throwing his nominee over the side of the Republican ship, the former leader of House conservatives presented GOP positions in much more credible and appealing fashion than the party’s nominee. Republicans can rest assured that it’s still possible to do that, even with Trump at the top of the ticket.

But therein lies the rub.

Trump is the Republican nominee, and his platform is a dystopic caricature of GOP positions. His style is offensive and bombastic and unacceptable for a candidate for the presidency of the United States, much less an actual commander in chief.

Kaine’s strongest moments in the debate were when he pointed out that Pence was essentially unwilling to defend the policy perversions and epithets that have faithfully erupted from Trump’s orifices like a flaming geyser of bile.

Pence pushed back when he felt he was on solid ground, but wisely chose to let much of it go. Trump has none of that discipline. Everyone knows it. The contrast is not helpful to him.

Pence took well-rehearsed and well-honed swipes at Clinton. Trump lashed out at her. That contrast wasn’t helpful to Trump, either.

Trump’s platform doesn’t add up. He rails about debt but would slash revenue without enough spending cuts to offset the loss of tax dollars — because there simply isn’t enough money available to cut. He would force Mexico to pay for a border wall, even though he could never get such a proposal through Congress or convince Mexico to go along.

He would create a junta to round up people who are in the country illegally but has no articulated plan for how to deport them. He says he’d be strong internationally, but has proposed no thoughtful means of combating ISIS, countering Russian aggression or withdrawing U.S. foreign and military aid to key allies without empowering America’s enemies and rivals for global power.

Kaine pointed out all of these contradictions, and yet Pence found a way to bridge most of the distance between Trump’s warped platform and a more reasonable framework for a new Republican administration. You can disagree with Pence’s positions and still think he sounded sane and rational. And that, too, was a terrible contrast for Trump.

Democrats should worry that Kaine, roundly considered one of the party’s smartest leaders, made such little progress in picking apart core Republican ideas or in unnerving Pence even when he succeeded in highlighting the thinness and incoherence of Trump’s actual platform.

It was a very bad night for Kaine, and a very good night for Pence — who clearly would like to be in the mix for 2020 if he and Trump don’t land in the White House next year.

Democrats should thank their lucky stars that Kaine’s subpar performance is about as meaningful to Clinton as the typical previous-question vote is to the outcome of legislation.

But Republicans should be cursing themselves — again — for letting Trump win their nomination. Pence showed what a credible Republican candidate looks like, and Trump ain’t it.

Roll Call columnist Jonathan Allen is co-author of the New York Times-bestselling Clinton biography “HRC” and has covered Congress, the White House and elections over the past 15 years.