Krugman:

Barack Obama offers incremental reform: regulation of insurers to prevent discrimination against the less healthy, subsidies to help lower-income families buy insurance, and public insurance plans that compete with the private sector. His plan falls short of universal coverage, but it would sharply reduce the number of uninsured.

Mr. McCain, on the other hand, wants to blow up the current system, by eliminating the tax break for employer-provided insurance. And he doesn’t offer a workable alternative.

Without the tax break, many employers would drop their current health plans. Several recent nonpartisan studies estimate that under the McCain plan around 20 million Americans currently covered by their employers would lose their health insurance.

As compensation, the McCain plan would give people a tax credit — $2,500 for an individual, $5,000 for a family — that could be used to buy health insurance in the individual market. At the same time, Mr. McCain would deregulate insurance, leaving insurance companies free to deny coverage to those with health problems — and his proposal for a “high-risk pool” for hard cases would provide little help.

So what would happen?

The good news, such as it is, is that more people would buy individual insurance. Indeed, the total number of uninsured Americans might decline marginally under the McCain plan — although many more Americans would be without insurance than under the Obama plan.

But the people gaining insurance would be those who need it least: relatively healthy Americans with high incomes. Why? Because insurance companies want to cover only healthy people, and even among the healthy only those able to pay a lot in addition to their tax credit would be able to afford coverage (remember, it’s a $5,000 credit, but the average family policy actually costs more than $12,000).

Incremental, of course, has a way of turning excremental awfully fast.