If you are following the debate over health care, you are now familiar with some of the major fault lines. Should there be a new public insurance plan, into which anybody can enroll? Should the government require that everybody carry insurance of some form? Should an independent but democratically accountable institute be setting criteria for what services insurers must cover? And so on.

But in arguing about these questions, here and in other venues, we are also getting ahead of ourselves. Another, more important problem should be commanding our political attention--a problem that, if unresolved, could undermine health care reform all by itself.

That problem is money.

Everybody knows that our health care system is full of wasteful spending. There's the waste from administrative overhead and the never-ending hunt, by insurers, for healthy beneficiaires. There's the waste from unnecessary, even harmful, medical services. If we could eliminate even some of that waste, it should free up a great deal of money--more than enough to subsidize insurance coverage for those people who can't afford it already. Get rid of the waste, in other words, and we can pay for universal health care.

But it will take many years to pinpint and then reduce most of that excess. That means the government must find some other source of money to pay for universal coverage, at least for the time being.

Exactly how much money the government will need to find still isn't clear; it will depend, in large part, on legislative details yet to be determined. How quickly do we try to make coverage universal--over the course of two years or, say, six? How generous are the benefits all plans must provide? And how should we account for possible savings from changes in the way we deliver medical care?

But it's safe to assume that guaranteeing solid insurance coverage for everybody--including both those who are now uninsured and those whose insurance coverage is unreliable--will cost more than $1 trillion over ten years. Many experts think it will cost a great deal more.

President Obama, in his budget outline, put forward two ideas for raising this money. One was a reduction in the income tax deductions upper-income Americans take for charitable contributions. The other was reforms to the health care system itself, including elimination of the excessive payments government makes to some private insurers participating in Medicare. 

But that only amounted to $634 billion, or around half (maybe less) of what it will take to get to full coverage--a fact Obama openly acknowledged. He pledged to work with Congress on finding the rest but, already, the task is proving more difficult than it first seemed. Even key reform allies, like Senate Finance Chairman Max Baucus, have indicated they don't like the deduction shift.

Baucus, along with other members of Congress, has raised some alternatives. And, as I (among others) have written before, the best source of funds may be the existing exclusion of employer health benefits from personal income taxes. The exclusion alone is worth more than the cost of even a generous universal coverage scheme. Even a partial reduction would yield hundreds of billions of dollars--which, alongside the easier-to-achieve health care system savings, would at least get us close to what we needed for full universal coverage.

But changing the exclusion invites strong political opposition. Unions representing workers with generous health beneifts, like the Teamsters, don't like the idea. Nor do many employers, because they don't want government doing anything to fiddle with existing insurance arrangements. On subtantive grounds, both positions seem to be pretty short-sighted; both labor and employers should benefit from reform, however it is financed. But their opposition is real all the same.

We could, of course, simply increase taxes on personal income--or impose a value-added tax, as many European nationas have. We could enact a cap-and-trade scheme, then channel some of the revenue into health care, or we could cut spending elsewhere. But these measures would be no easier to accomplish politically.

And that's the rub. At this point, financing health care reform isn't much of a policy challenge. There are plenty of options, many of them both progressive and economically sound. But it's a huge political challenge--and one, I fear, that too many liberals may be ignoring.

Where is the lobbying for Obama's charitable deduction shift--or, failing that, some other tax hike on the wealthy? Where is the advocacy for tapping the exclusion or, if that's too unthinkable, then creating some other viable revenue stream? 

It's terrific to see such passion behind the idea of a public insurance option, which--among other things--should drive down the prices of medical care and make universal coverage a bit more affordable. And it's important to defend the virtues of comparative effectiveness research, which--like a public plan--should help reduce the cost of care, partiuclarly over the long run.

But, as my grandmother would say, none of these things will mean bubkes if we don't come up with the money to pay for reform.

--Jonathan Cohn