By PAUL KRUGMAN — New York Times.

Remember those Republican boasts that they would turn health care into President Obama’s Waterloo? Well, exit polls suggest that to the extent that health care was an issue in Tuesday’s elections, it worked in Democrats’ favor. But while health care won’t be Mr. Obama’s Waterloo, economic policy is starting to look like his Anzio.

True, the elections weren’t a referendum on Mr. Obama. Most voters focused on local issues — and those who did focus on national issues tended, if anything, to go Democratic. In New Jersey, voters who considered health care the top issue went for Gov. Jon Corzine by a 4-to-1 margin; Chris Christie won voters who were concerned about property taxes and corruption.

Yet there was a national element to the election. Voters across America are in a bad mood, largely because of the still-grim economic situation. And when voters are feeling bad, they turn on whomever currently holds office. Even Michael Bloomberg, the mayor of New York City, saw his supposedly easy reelection turn into a tight race.

And challengers did well even if they had no coherent alternative to offer. Mr. Christie never explained how he can reduce property taxes given New Jersey’s dire fiscal straits — but voters were nonetheless willing to take a flier.

This bodes ill for the Democrats in the midterm elections next year — not because voters will reject their agenda, but because all indications are that a year from now unemployment will still be painfully high. And Republicans may well benefit, despite having become the party of no ideas.

Which brings me to the Anzio analogy.

The World War II battle of Anzio was a classic example of the perils of being too cautious. Allied forces landed far behind enemy lines, catching their opponents by surprise. Instead of following up on this advantage, however, the American commander hunkered down in his beachhead — and soon found himself penned in by German forces on the surrounding hills, suffering heavy casualties.

The parallel with current economic policy runs as follows: early this year, President Obama came into office with a strong mandate and proclaimed the need to take bold action on the economy. His actual actions, however, were cautious rather than bold. They were enough to pull the economy back from the brink, but not enough to bring unemployment down.

Thus the stimulus bill fell far short of what many economists — including some in the administration itself — considered appropriate. According to The New Yorker, Christina Romer, the chairwoman of the president’s Council of Economic Advisers, estimated that a package of more than $1.2 trillion was justified.

Meanwhile, the administration balked at proposals to put large amounts of additional capital into banks, which would probably have required temporary nationalization of the weakest institutions. Instead, it turned to a strategy of benign neglect — basically, hoping that the banks could earn their way back to financial health.

Administration officials would presumably argue that they were constrained by political realities, that a bolder policy couldn’t have passed Congress. But they never tested that assumption, and they also never gave any public indication that they were doing less than they wanted. The official line was that policy was just right, making it hard to explain now why more is needed.

And more is needed. Yes, the economy grew fairly fast in the third quarter — but not fast enough to make significant progress on jobs. And there’s little reason to expect things to look better going forward. The stimulus has already had its maximum effect on growth. Even Timothy Geithner, the Treasury secretary, admits that banks remain reluctant to lend. Many economists predict that the economy’s growth, such as it is, will fade out over the course of next year.

The problem is that it’s not clear what Mr. Obama can do about this prospect. Conventional wisdom in Washington seems to have congealed around the view that budget deficits preclude any further fiscal stimulus — a view that’s all wrong on the economics, but that doesn’t seem to matter. Meanwhile, the Democratic base, so energized last year, has lost much of its passion, at least partly because the administration’s soft-touch approach to Wall Street has seemed to many like a betrayal of their ideals.

The president, then, having failed to exploit his early opportunities, is pinned down in his too-small beachhead.

If the Democrats lose badly in the midterms, the talking heads will say that Mr. Obama tried to do too much, this is a center-right nation, and so on. But the truth is that Mr. Obama put his agenda at risk by doing too little. The fateful decision, early this year, to go for economic half-measures may haunt Democrats for years to come.