Josh Marshall is unsure:

Mitt’s got a tight and iffy pivot to make super fast and in a climate where it’s hard to break through and people may not be eager to walk through a campaign charnel house. But he has to make it in the next four weeks to prevent the difficult to imagine possibility that Newt could sweep the opening primaries.

"Difficult to imagine?" Just look at the polls. First Read likewise thinks that attacking Gingrich will prove difficult:

Here's why: the attacks themselves on Gingrich are not easy to sell. Why? Because he has one golden ticket with most conservative Republicans: he did it; he led conservative Republicans out of a 40-year desert. So no ONE thing (Freddie Mac, three marriages, health-care mandate, Pelosi/global warming, criticizing Paul Ryan) will take him down like it could for another politician. 

Nate Silver is on the same page. Mainly because of this:

Fivethirtyeight-1207-gingrichcredential-blog480

Yep, Gingrich has pure partisan cred that Romney cannot come close to. That's what people remember. What they don't remember is that within one year of taking over the Speakership, his approval rating was a dismal 31 percent, 63 percent of Americans said he was too extreme, and 60 percent said they could not trust him. In 1995, a full 80 percent of Americans said they would not like Gingrich to run for president.

It took him a year to implode as a public figure. Can you imagine him gaining on Obama in the next year the more people get to know him or remember the full picture? And recall this: even now, before any of that barrage of negative attacks, Obama beats Gingrich by the same margin he beat McCain.