There’s a lot we don’t know about what Mitt Romney would do if he won. He refuses to say which tax loopholes he would close to make up for $5 trillion in tax cuts; his economic “plan” is an empty shell.

But one thing is clear: If he wins, Medicaid — which now covers more than 50 million Americans, and which President Obama would expand further as part of his health reform — will face savage cuts. Estimates suggest that a Romney victory would deny health insurance to about 45 million people who would have coverage if he lost, with two-thirds of that difference due to the assault on Medicaid.

So this election is, to an important degree, really about Medicaid. And this, in turn, means that you need to know something more about the program.

For while Medicaid is generally viewed as health care for the nonelderly poor, that’s only part of the story. And focusing solely on who Medicaid covers can obscure an equally important fact: Medicaid has been more successful at controlling costs than any other major part of the nation’s health care system.