Give New York Times columnist Paul Krugman a little credit for pointing out the uncomfortable fact that Illinois Senator Barack Obama is campaigning against universal health care.

Krugman explained in Friday’s editions of The New York Times:

The central question is whether there should be a health insurance “mandate” — a requirement that everyone sign up for health insurance, even if they don’t think they need it. The Edwards and Clinton plans have mandates; the Obama plan has one for children, but not for adults.

Why have a mandate? The whole point of a universal health insurance system is that everyone pays in, even if they’re currently healthy, and in return everyone has insurance coverage if and when they need it.

And it’s not just a matter of principle. As a practical matter, letting people opt out if they don’t feel like buying insurance would make insurance substantially more expensive for everyone else.

Here’s why: under the Obama plan, as it now stands, healthy people could choose not to buy insurance — then sign up for it if they developed health problems later. Insurance companies couldn’t turn them away, because Mr. Obama’s plan, like those of his rivals, requires that insurers offer the same policy to everyone.

As a result, people who did the right thing and bought insurance when they were healthy would end up subsidizing those who didn’t sign up for insurance until or unless they needed medical care.

In other words, when Mr. Obama declares that “the reason people don’t have health insurance isn’t because they don’t want it, it’s because they can’t afford it,” he’s saying something that is mostly true now — but wouldn’t be true under his plan.

The fundamental weakness of the Obama plan was apparent from the beginning. Still, as I said, advocates of health care reform were willing to cut Mr. Obama some slack.

Krugman argues that it is time to stop cutting Obama that slack because the senator has begun defending his flawed plan by echoing right-wing talking points.

“Mr. Obama, who just two weeks ago was telling audiences that his plan was essentially identical to the Edwards and Clinton plans, is attacking his rivals and claiming that his plan is superior. It isn’t — and his attacks amount to cheap shots<"argues Krugman.

“First, Mr. Obama claims that his plan does much more to control costs than his rivals’ plans. In fact, all three plans include impressive cost control measures. Second, Mr. Obama claims that mandates won’t work, pointing out that many people don’t have car insurance despite state requirements that all drivers be insured. Um, is he saying that states shouldn’t require that drivers have insurance? If not, what’s his point?”

Obama’s point is, of course, a political one. He is trying, desperately, to position himself as the one serious challenger to Clinton. To do that, he must distinguish himself both from the national front-runner and from Edwards, who has attracted significant union and grassroots support with his economic populism.

Obama remains, in many senses, the most appealing Democratic contender. And there is good reason to believe that he could emerge in coming weeks as the most serious challenger to Clinton. He could, yet, be the Democratic nominee and the president.

But to do that, Obama must get serious about the major issues. It is not enough to just talk about “a different kind of politics.” Obama must practice it, and to do so he must develop coherent plans on issues such as health care.

Obama would not have had a hard time coming up with a better plan than that of Clinton or Edwards, both of which refuse to take the logical step of developing a universal, cost-effective and genuinely health-care oriented single-payer system, as Ohio Congressman Dennis Kucinich proposes.

But Obama has not tried to distinguish himself by being better than Clinton or Edwards.

Instead, as Krugman notes, “What seems to have happened is that Mr. Obama’s caution, his reluctance to stake out a clearly partisan position, led him to propose a relatively weak, incomplete health care plan.”

Rather than acknowledge the flaws in his own plan, Obama has attacked Clinton and Edwards in language that does indeed “sound like Rudy Giuliani inveighing against ‘socialized medicine.'” And Krugman is right to call the senator out on his wrongheaded approach.