Throughout the election campaign, when the two competitors talk about social insurance programs, they usually confine it to Social Security and Medicare, and really just Medicare. And it’s true that the Romney-Ryan plan for a voucher program instead of traditional Medicare would lead to higher premiums for most seniors.

But the planned growth rates for Medicare laid out by the Obama and Romney campaigns are actually the same: GDP + 0.5%. Both sides take different approaches to get there. But they plan to spend relatively the same amount on the program over time (the Romney campaign perhaps more, since they would repeal the “$716 billion in Medicare cuts” from Obamacare).

It’s on Medicaid where the two parties have the most difference, if you’re talking about social insurance. As the Obama campaign’s new ad makes clear, Romney would turn Medicaid into a dedicated block grant program, which would lower the amount of spending by up to 1/3. Importantly, that would impact the vast numbers of seniors who use Medicaid for nursing home care, which is why the above ad is framed that way. It takes a shot at Romney for raising nursing home fees 8 times, but then it gets to the core issue: if you cut Medicaid by 1/3, suddenly all those seniors who as dual eligibles used the nursing home coverage in Medicaid would not have that option. This “burdens families with the cost of nursing home care,” and these middle-class families actually are in no position to meet that burden.

You might suggest that the Obama campaign doesn’t have much of a record on this issue for differentiation. You would be wrong. The Affordable Care Act includes an expansion of Medicaid that would allow 16 million more low-income individuals into the system. That would unquestionably help defray the nursing home costs of more low-income seniors.

This chart above, via Kevin Drum, shows the difference pretty clearly. The level of spending on the health care safety net program for the poor veers almost entirely between Obama and Romney. And this ad shows that the Obama campaign has finally decided to make a fight on that point.

Of course, the Medicaid expansion is under threat, thanks to an adverse Supreme Court ruling. States could roll it back by themselves, and this represents a huge political fight for the next couple years. In addition, Medicaid could become part of grand bargain talks, although my impression was that there were forces inside the Administration that really defend Medicaid. After all, the expansion is a major part of the ACA, representing half of the coverage gains.

The point is that, even if Obama wanted to keep Medicaid spending constant, this would represent a huge difference with Romney. But he actually has signed legislation expanding it. If Medicaid doesn’t come up in the context of the safety net in tomorrow’s town hall-style debate, then somebody isn’t doing their job.