Just in time for tonight’s vice presidential debate, the Obama campaign has released an ad about a big government health care plan that Mitt Romney and Paul Ryan have in their crosshairs. But the ad doesn’t focus on Medicare, about which you’ve heard so much this election season. It focuses on Medicaid, about which far too little has been said. Although Mitt Romney and Paul Ryan have proposed to transform both programs, the changes and spending cuts they have in mind for Medicaid would probably be more devastating. And the poor wouldn’t be the only ones to feel it.

The main reason is a group that many people don’t associate with Medicaid: Senior citizens. Medicaid provides health insurance to low-income people and, at any one time, it does so primarily for non-elderly—mostly kids and their mothers. But two-thirds of the money that Medicaid spends goes to that minority of enrollees who are disabled or over 65, because they are the ones with really big medical bills.

Many of these people are “dual eligibles.” They use Medicare for their regular and acute medical expenses, whether it’s getting a routine checkup or treatment for a heart attack. They rely on Medicaid to pay the portion of the bills Medicare does not cover, like deductibles for hospitals stays. They also rely on Medicaid to pay for long-term care, whether it’s staying in a nursing home or having caregivers at their own homes. That last part is critically important. Staying in a nursing home is very expensive—like $70,000-a-year expensive, according to the Kaiser Family Foundation. Having part- or full-time assistance at home also runs into tens of thousands of dollars a year.

Many elderly Americans can’t pay those bills, at least not for any significant length of time. That’s when they turn to Medicaid. Today, 70 percent of people who live in nursing homes use Medicaid—many of them middle class people who, having burned through their savings, are as dependent upon the program as people who never had the money in the first place.

So what is Romney proposing to do?