This salvo from a Romney-linked Super PAC includes the charge that Newt Gingrich supported a health insurance mandate they call “the centerpiece of Obamacare.” The fact that it was also the centerpiece of Romneycare doesn’t appear in the advertisement. But Romney, now the underdog for the GOP nomination, has to scrap back by attacking Gingrich from the right. That includes a total embrace of the Paul Ryan plan to end Medicare, which incidentally is probably a source of Gingrich’s strength among the aging GOP base.

The reason this matters: It will give Dems a weapon in the general election against Romney. “In order to make this attack, Mitt Romney has now given himself ownership of the Ryan plan,” Jed Lewison writes. “Let me say that again: Mitt Romney is now one hundred percent committed to Paul Ryan’s proposal to end Medicare and replace it with vouchers.”

Paul Begala summed up the thinking among Dems today. “The fact that Mitt Romney would call for essentially ending Medicare should disqualify him from the presidency in the eyes of millions of middle-class voters,” Begala told Talking Points Memo, adding that the Ryan plan is “the most toxic, anti-senior, anti-middle-class proposal I have seen from a major political party in years.”

A couple things here. First of all, as I said, Gingrich has come to prominence in the GOP race in part by courting seniors. The average voting member in the GOP base was alive during WWII. Gingrich has been completely careful rhetorically not to alienate them with proposals that appear to slash Medicare. He has retreated to his “wither on the vine” position from the mid-1990s: he would give seniors a choice between premium support and the fee-for-service plan, with the expectation that more people would choose premium support (I have no idea why he thinks this). The thing is, this was Romney’s position as well, though his attacks on Gingrich for criticizing the Ryan plan, necessitated by his imminent defeat, have now taken prominence.

Second, Romney or whoever comes out of the GOP nomination will still have a plausible line of attack against Obama on Medicare, on a couple levels. First, they will put forward what they offered in the 2010 elections, that the Affordable Care Act cut Medicare by $500 billion. This is largely untrue, but it happened to work in 2010. Second, all of the proposals to cut Medicare that Obama put out during the debt limit debate will come back with a vengeance in attack ads. I don’t think this is as clean a shot as Democratic operatives think.

Anyway, enthusing over Romney stepping in the Ryan plan seems to me like fighting the last war. Romney will not be the nominee if things go the way they have the past several months.