Honestly, Gingrich needs to go hard after Santorum in the debate on Wednesday, rather than focus on Romney, which he'll probably try to do. The only way Gingrich can still win is if he completely deteriorates Santorum enough to once again by the "Anti-Romney" choice. He's not going to be able to make this a two-way race between himself and Santorum, try as he might.
Gingrich can't win. All he can do right now is affect which of Romney and Santorum win. So it's no surprise that a Romney supporter is saying he needs to attack Santorum, just as I hope he'll attack Romney. Personally, I think Newt's focus will be on attacking the media again.