Until Thursday night, GOP presidential candidate and former Pennsylvania Sen. Rick Santorum blended into the wide field of candidates vying for the nomination. But Santorum stepped up at the Orlando debate, attacking front-runner Rick Perry on his immigration record and vowing to re-instate “don’t ask, don’t tell” if elected.

He seems to have made an impression. “Last night was an opening for candidates like Santorum,” Florida Republican Harlan Mason of St. John’s County said today, “and he stood out.”

Former Florida GOP Chairman Al Cardenas, who is also chairman of the American Conservative Union, said today the “message of last night’s debate was: ‘Not so fast,’” pointing in particular to what he thought were strong performances from Santorum, Newt Gingrich and Herman Cain. 

In one of the night’s more memorable exchanges, Santorum challenged Texas Gov. Perry’s record on illegal immigration. Specifically, he targeted Perry’s support of in-state tuition rates for children of illegal immigrants. Perry defended his program, prompting an attack from Santorum.

“No one is suggesting up here that the students that are illegal in this country shouldn’t be able to go to a college and university,” Santorum said. “I think you are sort of making this leap that, unless we subsidize this, the taxpayers subsidize it, they won’t be able to go.”

He added, “Why should they be given preferential treatment as an illegal in this country?”

The comment garnered applause from the audience. Santorum said of Perry, “Yes, I would say that he is soft on illegal immigration.”

Santorum has consistently billed his campaign and candidacy as the one true conservative in the race, taking hard-line stances on fiscal policy, immigration and social issues. Not unexpectedly, Santorum received an online question regarding the repeal of  “don’t ask, don’t tell” from a gay soldier serving in Iraq.

In response, Santorum said, “Removing ‘don’t ask, don’t tell,’ I think, tries to inject social policy into the military. And the military’s job is to do one thing, and that is to defend our country.”

Santorum restated his commitment to the policy that bars gays and lesbians from serving openly, saying, “Going forward, we would reinstitute that policy, if Rick Santorum was president, period.”

Santorum defended his stance this morning on “Fox and Friends,” going so far as to say that the repeal of “don’t ask, don’t tell” will affect the military’s ability to enlist volunteers.

 ”We haven’t begun to see what the  consequences of going to ‘don’t ask, don’t tell’ are going to be,” Santorum said. “A lot of people, I believe, are going to leave. I think a lot of folks are not going to join who otherwise would have joined. And that’s going to hurt our readiness, it’s going to hurt our ability to defend this country and we shouldn’t be playing social experimentation.”

In an email to his supporters after Thursday night’s debate, Santorum touted his performance, asking for special contributions. “We’re facing a fundraising deadline in just seven days and your expedited contribution will ensure we have the resources needed to share our conservative views,” he wrote.

While Santorum’s candidacy remains a long shot, he hopes he can continue to build on the momentum he gained in Thursday night’s debate.

ABC News’ Amy Walter contributed to this report.