Actually, that is not accurate. Keeping it only to the primary season, Newt has said on the debate stage, that Santorum was out there in front on Iran, and leading the way on that issue, when people seldom give him (RS) credit for that. He said good things about Perry, while Perry was still running, and I am sure there are others...
Rick Santorum is too insecure to say anything nice or laudatory about any of his opponents... and has taken quite a few immature nasty shots at Newt, who was Santorum’s mentor...
As far as Newt endorsing himself, how many times (honestly) have you heard Santorum say, “I’m the only candidate who... fill in the blank”...? Honestly? Then, of course, when God Himself has called you to run, as Santorum has told his supporters, there’s no need to endorse yourself. much.
It was a joke. I remember him endorsing DeDe.
On the other hand, so far as I can ascertain, he endorsed NOBODY in the critical 2008 presidential election, where there were several conservative candidates who might have benefited from an endorsement by the bearer of the Ronald Reagan Torch.