Donald Trump and Hillary Clinton during their third and final debate at UNLV in Las Vegas on Oct. 19. (Carlos Barria/Reuters)

The third presidential debate included an exchange in which Donald Trump defended his business skills against Hillary Clinton’s attacks. “If we could run our country the way I’ve run my company, we would have a country that you would be so proud of,” he said. “You [Clinton] would even be proud of it.”

This was a small moment in the debate (which was already well into “you’re a puppet!” territory), but it raises an interesting point. Trump’s managerial acumen has been a big part of the case for his election. During the Feb. 25 Republican primary debate, for instance — otherwise mostly notable for “unintelligible yelling” —  Trump said that “the wall is $10 billion to $12 billion, if I do it. If these guys do it, it’ll end up costing $200 billion.”

My point is not to argue about whether Trump is in fact a great executive; for the purposes of this post, let’s stipulate that he is. I’m more interested in his claim — a staple of many campaign seasons — that private sector management skills translate automatically into making government more efficient and effective. The claim, in short, that government can be run as a business. But as Prof. Wallace Sayre quipped back in the 1950s, “business and government administration are alike in all unimportant respects.”

A useful case study here is another project Trump cited frequently on the campaign trail, which earned an entire chapter in “The Art of the Deal”: the rebuilding of the Central Park skating rink in New York in the 1980s.

After six years and some $13 million, New York had failed to renovate the rink. Trump said he could do the job in six months, instead, and did so — ahead of schedule, and under budget. In a November 2015 interview with Bloomberg, Trump called the rink “an example of what can be done by private enterprises.” Asked how it linked to the governmental arena, even to being commander in chief, he replied that “It’s all the same. It has to do with efficiency, it has to do with common sense, it has to do with knowledge.”

This provides a good excuse to make one of my regular plugs for the work of the late, great political scientist James Q. Wilson.

In his 1989 book “Bureaucracy: What Government Agencies Do and Why They Do It,” Wilson examined the lessons we might take from the rink project. He noted that Trump had several sizable advantages over public sector managers — notably that the city had to work within a variety of constraints. These existed to fight corruption, ensure equity and enhance transparency — in short, to provide good government.

The city had to put out every part of the contract publicly out to bid, and accept the lowest bidder regardless of whether they actually had the needed expertise. In fact, as Wilson notes, the city was prohibited by law from even discussing the project in advance with potential bidders. Every part of the project had to be negotiated in writing in advance, and any changes on the fly renegotiated and re-contracted.

The city also had to worry about multiple constituencies who wanted many incompatible things — cold ice and environmental protection, say. (The project began in the wake of the Arab oil embargo, one reason it originally chose a brand-new type of refrigeration system that wound up failing.)

New York need to achieve multiple goals, then — only one of which was actually building a functional rink. “When we complain that contracts were awarded without competitive bidding or in a way that allowed bureaucrats to line their pockets, we acknowledge that we care about many things besides skating rinks,” as Wilson points out.

This takes nothing away from Trump’s achievement in Central Park. But it does make clear that as president he would have to deal with far more constraints on his managerial desires than he does as a private sector chief executive.

Efficiencies in governmental processes are surely possible and desirable, but success as president is not simply about turning a profit. That makes “success” hard to measure in the first place. And it also highlights the nature of the public sector balance sheet. Profit is usually privatized — while risk, and the cost of public goods, is socialized.

At a conference in Pittsburgh last week, President Obama noted that “part of government’s job … is dealing with problems that nobody else wants to deal with.” Caring for our most vulnerable neighbors is a costly affair — “liabilities on the public ledger,” as LA Times columnist Michael Hiltzik recently put it. “But in the long run, they’re assets, because they testify to the cohesiveness of society, which is priceless.”