Hillary Clinton opened fire on Barack Obama across an array of issues, but saved the really big guns for health care: "Of all our differences," said Hillary in Rhode Island (the forgotten primary state), "the one that is just inexplicable to me is his refusal to put forth a plan on universal health care and his continuing attacks on my plan to do so."

How hard can it be to offer a universal health care plan? "John Edwards had a plan, I had a plan, Chris Dodd had a plan, Dennis Kucinich had a plan, Bill Richardson had a plan. Because we're Democrats ..." Clinton said.

But Obama, in his Bob the Builder campaign designed to appeal to the toddler in every American, offers a plan that is all gain and no pain: subsidized health insurance for anyone who wants to buy it, whenever they want to buy it. More money, more choice, no cost. Gee, what's not to like?

Nothing, except that Hillary is correct. Obamacare can't possibly work, because it doesn't make sense to buy insurance when you are young and healthy if you are guaranteed access anyway when you are older and sicker.

And that's the problem.

The exchange between the two Democrats highlights the dirty little secret that not even Hillary will tell you about a universal government health insurance program. The problem with our current system that mandatory national health insurance will solve is not that people don't get health care -- it's that they don't pay for it.

Young healthy folks are more and more likely to go without health insurance. That means the pool of insured people is older and sicker and, therefore, more expensive to insure. Health insurance premiums rise, which makes health insurance an even worse deal for the relatively young and healthy, guaranteeing that more and more twentysomethings are uninsured, and health insurance costs for us middle-aged and older folks skyrocket.

What kind of people in the U.S. are uninsured? A whole lot of people like Brandy Coons, a 23-year-old Atlanta waitress highlighted on the front page of The New York Times as the new face of the "free rider" problem. Brandy admits she could probably afford a policy if she cut back on her gym membership and her photography hobby, but why should she do that?

"I'm young and in pretty good shape ... The insurance premium was more than what I would pay for my prescriptions, so I just decided not to deal with it," Coons said.

But even The New York Times cannot admit the real "free rider" problem here. It's not that the health care needs of uninsured twentysomethings like Brandy are bankrupting the system. It's that not enough twentysomethings like Brandy are paying for the health care of fortysomethings and older. That's the only way insurance makes sense: We pay into it when we are young and healthy, and we get something out of it when we are older and more likely to get sick.

But try running on that as your platform: Make the young people pay more!

Here's the other dirty little secret: National health insurance is going to cost Brandy and other taxpayers a whole lot more than either Hillary or Obama admits. Just ask Gov. Deval Patrick in Massachusetts, where just two years into operation, the state's mandatory health insurance plan is already costing $400 million more than budgeted.

Meanwhile we have a Medicare system that is going to go bankrupt.

Here's a question neither Hillary nor Barack will answer: How can we justify spending billions to insure the Brandys of the worlds, when we haven't yet secured the health care financing for our existing promises to senior citizens?