Depending on what poll you like, Mitt Romney has either erased Newt Gingrich’s lead or not. What we do know is that since South Carolina, Romney has gone from playing defense (on taxes, on Bain) to playing offense (challenging Gingrich on his speakership, his ethics problems, his influence-peddling and even his demand to have a cheering section at debates).

Interestingly, Romney hasn’t attacked, at least not yet, on Social Security, a topic on which Gingrich is vulnerable. Gingrich is essentially ducking all the hard issues and, unlike Romney, has not proposed a plan for shoring up Social Security. Romney has made clear he’ll look at both the retirement age and indexing benefits according to income, but not tax increases.

What has Gingrich done? Propose two gimmicks, neither of which address Social Security’s insolvency problem. As Rick Santorum pointed out, Gingrich’s idea for going to individual accounts would require billions more in funding, which means billions more borrowed from China.

Ramesh Ponnuru agrees with Santorum:

Plenty of Social Security plans involve the government saving money in the long term by taking a hit in the present. Gingrich has managed to devise a plan that actually increases the program’s long-term cost. The price tag for Gingrich’s originality, based on estimates of similar proposals in years past, would be several trillion dollars. The plan simply assumes that spending on the rest of the budget will be cut so dramatically, and the increased national saving will so boost economic growth and thus tax revenue, that we will be able to afford a much-larger Social Security program.

Gingrich’s other idea was taken from Texas Gov. Rick Perry: allowing states to opt out of federal Social Security. He sometimes refers to this as the Galveston Plan. However, as previously reported, this idea is fraught with problems and does nothing to help the existing system’s solvency.

In particular, the idea makes no sense for the state of Florida. In a white paper put out when Perry first waded into this topic, the Romney campaign argued the plan would be a fiscal nightmare for Florida if it attempted to take over retirement benefits from the feds:

If it attempted to pay benefits to its large number of retirees while only collecting existing payroll taxes from its workers, Florida could be saddled overnight with a $16 billion budget gap. This could impose an immediate and severe financial crunch on a state that has had tremendous difficulty balancing its budget even without carrying social security obligations. This year, Florida was forced to close a $3.8 billion shortfall, and Governor Rick Scott vetoed an additional $615 million in state spending. An additional $16 billion gap is so large that even eliminating funding for Florida’s entire public education system ($11.9 billion) and prison system ($2.2 billion) would not be sufficient to bring the budget back into balance.

More plausibly, Florida would need to raise taxes to pay for the additional burden. Florida currently has no income tax. To raise $16 billion a year, it would almost certainly need to institute one. It might also have to raise its sales tax far above its current level of 6 percent. Alternatively, to stay solvent Florida could raise its retirement age and/or lower the benefits it pays to current seniors. The deficit could require either kicking more than one million individuals off of the program or cutting benefits by more than $4,000 per person per year.

In short, sending Social Security to the states was a bad idea when Perry proposed it, and it’s a bad idea, especially in Florida, now that Gingrich has embraced it.

Perhaps both Romney and Santorum will get around to this issue. In both cases, the candidates cannot be accused of grandstanding or scaring seniors since they have behaved responsibly in offering their own plans. Santorum has even gone so far as to propose cutting current retirees’ benefits, which goes beyond what Rep. Paul Ryan (R-Wis.) and the Simpson-Bowles Commission recommended. Gingrich, however, can legitimately be attacked for punting on a critical issue and behaving irresponsibly. Will one of his opponents bring it up? Stay tuned.