IMHO you can trace his fall to when he started attacking Romney for being too harsh on illegals. Newt had already gotten into trouble early on with his Perry-esque warning to conservatives for not being “humane” to illegals that had been here a long time. It even got the “FUNG” from Jim Robinson himself.
Later, when it appeared no other candidate had a shot at stopping Romney, many of us held our noses at the Newt/Pelosi couch commercial on globull warming and his multiple wives and...like Jim...went all in on Newt.
After Santorum won Iowa, it seemed that there was another possibility that did not require as much nose holding. Support started to shift, Newt had a bad debate with moonbases, and then the attack on Romney for being too harsh on illegals. It brought back all the amnesty talk and gave Mittens cover so he could pretend to be conservative.
After Jims announcement of support for Newt and his warning about attacking the remaining conservatives in the race, many Newt doubters held their tongues. The constant attacks on (in their words) “Reverend Rick”, “Little Ricky” etc etc has caused more and more freepers to be more open about their doubts about Newt. Attacks about morality not being important anymore and the recent cheering by some anti-rick noobs about Romney catching up to Santorum has caused more of the Newt doubters to speak out in the open.
Just my 2 cents. I want Romney stopped. Whether its Santorum or Newt that does it.
I think you nailed it exactly on the head.