For his part, the former Massachusetts governor kept his focus on Barack Obama.
"We've got a president in office three years and he does not even have a jobs plan yet," Romney said. "I've got one out there already and I'm not even the president yet."
Newt Gingrich softened his attack on Romney and also focused on the president.
"It tells you everything you need to know about the difference between Barack Obama and the five of us: we actually think work is good," Gingrich said.
On the subject of negative campaigning, Ron Paul, who is coming off a strong second place win in New Hampshire, took a shot a Santorum.
"There was one ad we used against Sen. Santorum and the only problem was I couldn't get everything I needed to say in one minute," Paul said.
Huntsman left the race Monday without ever making much of a splash. In one poll, he even trailed a comedian.
"I believe it is now time for our party to unite around the candidate best equipped to defeat Barack Obama," Huntsman said during his announcement.
That candidate, Huntsman says, is Romney.
Many Republicans now say if Romney wins South Carolina, the GOP race is over. Monday's Fox News debate was a crucial last stand for the other candidates.
The South Carolina primary is on Jan. 21.