In March, House Budget Committee Chairman Paul Ryan (R-Wis.) took a not-so-subtle shot at Mitt Romney’s record on health care in the context of the 2012 presidential campaign. “It’s not that dissimilar to ObamaCare,” Ryan said of Romney’s reform law in Massachusetts. “And you probably know I’m not a big fan of ObamaCare.”

Now, however, the right-wing Wisconsinite is singing a different tune. Asked about the striking similarities between Romney’s and Obama’s reform laws, Ryan said this week, “I don’t think this question matters that much anymore.”

It speaks to what I consider the biggest surprise of the presidential race so far: Romney is simply getting a pass on health care. The former governor’s health care included an individual mandate forcing taxpayers to purchase insurance; it provided benefits to immigrants who entered the country illegally; and it covers abortion — and somehow, this hardly ever comes up in the middle of the GOP primary contest. A year ago, the right was saying Romney wouldn’t even be considered unless he renounced and apologized for his health care law, and now, it’s effectively become a non-issue.

Jonathan Bernstein had a good piece the other day, referencing the last Kaiser survey data on health care, and concluding that Romney’s GOP rivals are “blowing it.”

First, the context: as you might expect, Republicans really hate Barack Obama’s health care reform, with an 11/81 split against it and almost two-thirds “very unfavorable.” And those who know about the Massachusetts plan have a similar opinion, which isn’t strange since the basic structure is so similar (although lacking the important ingredient of Barack Obama, as I’ve argued): Republicans oppose Romneycare by a 6-1 margin.

But the key number isn’t how many Republicans dislike health care in Massachusetts; it’s how many don’t know enough to offer an opinion. That would be a whopping 77% (and even more telling, it’s the same number for likely primary voters as it is for all Republicans in the survey). Kaiser also asked about whether the Massachusetts reform was similar to the national reform law, with the same results: 69% of likely primary voters didn’t have an opinion. Of those who did, 18% said it was similar while 11% thought otherwise.

So here we are, just 10 weeks from the Iowa caucuses, and Mitt Romney’s opponents have so far completely failed to let Republican voters know about his (presumably) biggest weakness.

At least in the primary phase, this was supposed to be a weight on Romney’s shoulders. How could he run for the Republican nomination after providing the blueprint for the health care law that the GOP hates with the heat of a thousand suns? How could Republican voters condemn government health care mandates to be the most offensive policy in American history, and then nominate for president the only governor in America to impose a health care mandate on his constituents?

But these details only make a difference if someone tells GOP voters about it. At this point, it looks like “Romneycare” is a hanging curve, right over the middle of the plate, but the rest of the Republican field just doesn’t want to swing.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.