Santorum is a very good debater. He realizes he is in danger of becoming a second tier candidate and now that there are only four candidates left "second tier" is very thin. When asked about Gingrich's suggestion that he get out of the race Santorum pointed to his first place finish in Iowa and coming in ahead of Gingrich in New Hampshire. He came very close to calling Gingrich crazy.
Twice he and Gingrich got into private one-on-one arguments which worked for all of the candidates because the remaining four candidates are all pretty good at this.
Ron Paul was asked about programs for veterans returning from Iraq and Afghanistan. He recounted the post-World War II era saying there were no government programs to deal with the 10 million returning veterans. Gingrich pointed out the benefits of the GI Bill.
Ron Paul wasn't the crazy uncle in the basement as he was on Monday and he probably didn't move a single vote. He'll get what he gets and he'll stay in this race through June.
No one tripped over themselves, everyone seemed to be relaxed and informed.
The overall answer is: In a very odd way, this debate didn't live up to its advance billing - at least the billing here in South Carolina - where it was assumed this was going to be bare-knuckled, steel-cage, death match.
I can't imagine any votes changed as the result of this debate. Let's go back to eight people on the stage.