By Paul Krugman. New York Times.

One general rule of modern politics is that the people who talk most about future generations — who go around solemnly declaring that we’re burdening our children with debt — are, in practice, the people most eager to sacrifice our future for short-term political gain. You can see that principle at work in the House Republican budget, which starts with dire warnings about the evils of deficits, then calls for tax cuts that would make the deficit even bigger, offset only by the claim to have a secret plan to make up for the revenue losses somehow or other.

And you can see it in the actions of Chris Christie, the governor of New Jersey, who talks loudly about acting responsibly but may actually be the least responsible governor the state has ever had.

Mr. Christie’s big move — the one that will define his record — was his unilateral decision back in 2010 to cancel work that was already under way on a new rail tunnel linking New Jersey with New York. At the time, Mr. Christie claimed that he was just being fiscally responsible, while critics said that he had canceled the project just so he could raid it for funds.

Now the independent Government Accountability Office has weighed in with a report on the controversy, and it confirms everything the critics were saying.

Much press coverage of the new report focuses, understandably, on the evidence that Mr. Christie made false statements about the tunnel’s financing and cost. The governor asserted that the projected costs were rising sharply; the report tells us that this simply wasn’t true. The governor claimed that New Jersey was being asked to pay for 70 percent of a project that would shower benefits on residents of New York; in fact, the bulk of the financing would have come either from the federal government or from the Port Authority of New York and New Jersey, which collects revenue from residents of both states.

But while it’s important to document Mr. Christie’s mendacity, it’s even more important to understand the utter folly of his decision. The new report drives home just how necessary, and very much overdue, the tunnel project was and is. Demand for public transit is rising across America, reflecting both population growth and shifting preferences in an era of high gas prices. Yet New Jersey is linked to New York by just two single-track tunnels built a century ago — tunnels that run at 100 percent of capacity during peak hours. How could this situation not call for new investment?

Well, Mr. Christie insisted that his state couldn’t afford the cost. As we’ve already seen, however, he apparently couldn’t make that case without being dishonest about the numbers. So what was his real motive?

One answer is that the governor is widely assumed to have national ambitions, and the Republican base hates government spending in general (unless it’s on weapons). And it hates public transportation in particular. Indeed, three other Republican governors — in Florida, Ohio and Wisconsin — have also canceled public transportation projects supported by federal funds. The difference, of course, is that New Jersey is a densely populated state, most of whose residents live either in Greater New York or Greater Philadelphia; given that position, public transit is the state’s lifeblood, and refusing to invest in such transportation will strangle the state’s economy.

Another answer is that canceling the tunnel allowed Mr. Christie to divert funds from that project — as his critics have said, to cannibalize the investment — and put them into the state highway fund, thereby avoiding the need to raise the state’s tax on gasoline. New Jersey gas taxes, by the way, are lower in real terms than at any point in the state’s history. But, as a candidate, Mr. Christie said that he wouldn’t raise those taxes, so cannibalizing the tunnel helped him avoid embarrassment.

The crucial point about both of these explanations is that they stand Mr. Christie’s narrative about himself on its head. The governor poses as a man willing to make hard choices for the future, but what he actually did was sacrifice the future for the sake of personal political advantage. He catered to national Republican prejudices that are completely at odds with New Jersey’s needs; he cared more about avoiding embarrassment over a misguided campaign pledge than about serving an urgent public need.

Unfortunately, Mr. Christie’s behavior is all too typical these days.

America used to be a country that thought big about the future. Major public projects, from the Erie Canal to the interstate highway system, used to be a well-understood component of our national greatness. Nowadays, however, the only big projects politicians are willing to undertake — with expense no object — seem to be wars. Funny how that works.