In New Jersey, a moral drama is unfolding. Governor Chris Christie has presidential ambitions. He'd like to be as popular as possible with Republicans voters in important primary states like New Hampshire, Iowa, and South Carolina. He'd also like to do the right thing—or at least be seen as doing the right thing—when a piece of legislation crosses his desk, demanding a signature or veto.

And those desires are now in conflict.

There's an animal-welfare bill on his desk. Its premise is that slaughtering pigs to be consumed as carnitas or prosciutto or bacon or ham hocks is fine (if not quite kosher), but that confining pregnant pigs to an enclosure so small that they can't even turn around for as long as two and a half years is straightforwardly cruel and immoral.

Signing this law would be unpopular in Iowa, where there are more than 20 million pigs, and pork producers who stand to lose a lot of money if forced to house them more humanely, and who get nervous when government regulators meddle in livestock practices. Signing the bill may well hurt Christie's chances in the Iowa caucuses. Is it nevertheless clear that signing the law is the right thing to do?

Uncommonly so.

Christie has no principled objection to laws against animal cruelty. The New Jersey Legislature, which has studied the matter in much greater depth than the governor, passed the bill by an overwhelming margin and with bipartisan support, even though Christie vetoed an almost identical bill back in 2013. New Jersey voters also support the legislation by a wide margin.

There may be times when a governor ought to veto a bill despite broad support in the legislature and among the people, but this isn't a subject where Christie has special expertise, or a coherent principled objection, or even a plausible counterargument. And it is a case where he has a clear political conflict of interest. In other words, it's the quintessential case where a veto is inappropriate.

What's more, the position taken by the New Jersey Legislature and Garden State voters is strong on the merits. "It’s not hard to understand the argument—it simply makes intuitive sense that forcing animals to spend almost their entire lives immobilized constitutes cruelty," Bruce Friedrich writes in National Review. "But animal scientists have looked closely at the crates to detail the concerns, and they fall into two categories: mental and physical. Pigs are smart animals—they outperform both dogs and cats on tests of behavioral and cognitive sophistication. In fact, they play rudimentary video games with more success than chimpanzees, our closest living relatives. So just as our dogs and cats would if they spent virtually their entire lives unable to even turn around, the pigs go insane from the stress. And just as would happen to any animal if she were unable to move for months at a time, pigs’ muscles and bones deteriorate from lack of use."

Below is a video about these enclosures produced by The Humane Society of the United States. Turn down the volume and just look at the images to get a sense of how these pigs are confined. Would you say that it constitutes needless animal cruelty?

There are ways that Christie could rationalize a veto. He might think to himself, "There are so few pigs in New Jersey, and many that are here aren't even kept in these enclosures. Besides, I'll be gone soon enough, and the next governor can sign this bill. And just think of how much good I can do if I make it to the White House!"

My instinct as a voter is to punish politicians who let themselves think that way. At bottom, the logic is that advancing their ambitions serves the public interest, a rationalization responsible for all manner of immoral mischief in U.S. politics. If Christie vetoes this bill without an explanation stronger and more coherent than anything he has offered in the past, it will be fair to conclude that the reputation he's cultivated as a man willing to take on special interests to advance commonsense reforms is not what voters will get if they put him in the White House.