Santorum did not endorse Gingrich in Florida, nor would I expect Gingrich to do so in Michigan. But Santorum didn’t run any ads in Florida, and his SuperPac didn’t run any ads either. He certainly didn’t run ads attacking Gingrich in Florida. He wasn’t even IN florida for several days, he went home, and then went out to try to slow Romney in Nevada.
That’s all I would expect from Gingrich — not to run ads attacking Santorum in Michigan, and for his SuperPac not to attack Santorum in Michigan. Gingrich can’t win Michigan, he’s not competing there, so if they were to attack Santorum there, it would only for one purpose — to give Romney the win in Michigan.