(Manuel Balce Ceneta/Associated Press)

But in a call this morning, Romney surrogates emphasized the candidate’s strong support for House Budget Chair Paul Ryan’s Medicare reform plan, the one that would replace the traditional entitlement program with one that gave seniors vouchers to purchase private polices. “Governor Romney recognized right away the features of that plan,” said Romney-backer John Sununu.

In siding with the Ryan plan, the Romney campaign looks to draw a contrast with former speaker Newt Gingrich, who has criticized the policy as, among other things, “right-wing social engineering.” The strategy, pollsters say, also runs a big risk: Alienating a seniors, a key swing demographic, on what’s likely the election’s most crucial health care debate.

“Seniors vote, they vote at higher rates, and Medicare is the health care voting issue of our time,” says Brodie. “Because it’s a complex policy topic, there’s a lot of room for the way language and terms to get a certain effect. We’ll likely see poll results all over the board depending on what language is used.”

Medicare is going to matter in the 2012 election, likely more so than the health-reform law. We already know where the candidates stand on the Affordable Care Act: President Obama wants to keep it, every Republican contender wants to repeal it. Those positions won’t change before November, nor will they do much to change voter opinion. Both parties have made their case on health reform for 18 months now, but public opinion still looks pretty similar to when the law first passed:

A lot of where those crucial seniors land will depend on how Republicans manage to frame the idea of vouchers in Medicare. Right now, it’s actually a bit of a blank slate. When the Kaiser Family Foundation polled on the idea of Medicare vouchers in April, right in the heat of the debate over Ryan’s proposal, it found that two-thirds of voters either hadn’t heard about the idea, or didn’t know what it meant. Opinion varied greatly depending on how information on the Medicare plan was presented:

The best way to frame Medicare vouchers, pollsters say, is by presenting it as another choice, while traditional Medicare remains intact. “The absolute first thing is having Medicare as a choice,” says Robert Blendon, professor of health policy and political analysis at Harvard. “It’s a very dramatic thing to say we’re going to substitute for Medicare.”

That sounds a lot like Romney’s actual plan, which, unlike Ryan’s, would include traditional Medicare as an option. It sounds a lot like how Republican strategist Frank Luntz defended vouchers on the Diane Rehm show recently, describing the issue as about “rights of control,” asking “What’s wrong with giving people more control over how they use their health-care dollars? What’s wrong with giving them the right to choose the doctor, the hospital, the medical plan, the prescription drug plan?”

What that does not, however, sound like, is what Romney is saying Thursday. Endorsing Ryan without drawing much contrast “allows the other side to say you want to eliminate Medicare,” says Blendon. “No matter what, Democrats are going to see an opening here to say Republicans are trying to undermine Medicare. If somebody mentions Medicare and private accounts in the same plan, that’s a bit less threatening.”