If the previous Republican presidential candidate debate saw businessman Herman Cain use his newfound popularity to go on the offensive about his 9-9-9 Plan—a flat tax that would convert or add a nine percent to income, corporate, and sales taxes—then last night’s debate was where Cain was largely forced to go onto the defensive about the tax and his other policies.

Still, when CNN’s Anderson Cooper tried to get a straight answer out of Cain on his border security proposal, there wasn’t much pressure on the candidate to answer to his joking-but-not-joking suggestion that he’d put up a lethal electrified fence along the U.S.-Mexico border.

In fact, the other candidates largely agreed with his response to Cooper: "Allow me to give the serious answer. I think we should secure the border for real, including a fence, technology, and boots on the ground in the more dangerous areas."

It wasn’t clear whether "technology" meant electricity, and Cooper didn’t press him on the question. He did press Cain on whether he meant a fence along the entire border—something Texas Gov. Rick Perry said would take 10 to 15 years and cost $30 billion. Both Cain and Minnesota Rep. Michele Bachman agreed that the entire border should be fenced—Bachmann insisted on "a double-walled fence," at that—but Perry said border security could be maintained with "boots on the ground" and "strategic fencing."

Cain has faced some fairly intense scrutiny over the last few days after he said, about the border fence, "It’s going to be 20 feet high. It’s going to have barbed wire on the top. It’s going to be electrified. And there’s going to be a sign on the other side saying, ‘It will kill you—Warning.’"

He initially backed away from that statement, calling it a joke, before telling reporters in Arizona, "it might be electrified."

Cain’s statement was the tipping point for one Latino GOP activist, who recently and publicly resigned from the party in Texas. And the man, Lauro Garza, told TPM he doesn‘t think Cain was kidding at all: "I have allegedly pro-life Republicans telling me that advocating for the murder of people crossing the border is a perfectly reasonable thing to do. We took Herman Cain’s remark very seriously because it was the second or third time he had said similar things."

"Our last best hope was Rick Perry, even though we knew he was a very leaky vessel," Garza said, referring to Perry on immigration. "We had no choice but to hang the last of our hopes on him and he dashed them immediately." Perry’s decision to walk back his "heartless" comment on in-state tuition for immigrant children ended Garza’s support of the candidate.

On the 9-9-9 Plan, Cain was pushed onto the defensive, and mostly just doubled down on the superiority of the plan. When other candidates and Cooper questioned him on how it would work and pointed out that expert analysis of it showed it would raise taxes on the middle class, Cain responded, "None of my distinguished colleagues who have attacked me tonight understand the plan."

He added, more than once, "I invite every American to do their own calculations."

But Cain was apparently flustered when asked about terrorism. While, during the debate, he said he could see himself negotiating with Al-Quaeda—a statement that was immediately pounced on by Bachmann—he later told Cooper: "I misspoke. Because I didn’t, you know, things are moving so fast, I misspoke. I would not do that, I simply would not do that."

Of the other candidates, Romney seemed to settle into his role as co-frontrunner, coming off as calm and reasoned—and knowing when to criticize other candidates. Perry, who appeared sluggish in the last debate, woke up, but at his most animated mostly seemed furious at his place in the debate—including one angry exchange he had with Romney where he accused Romney of "hiring illegals" to work at his home.

Former Speaker of the House Newt Gingrich and Bachman attempted to keep up—Bachmann frequently called Cooper’s name from off-camera and was largely ignored. Santorum and Paul interjected when asked questions, but were far from the focus of the debate. And John Huntsman boycotted the debate because the New Hampshire primary—the first in the nation—is being threatened and he’s poured most of his resources into the state.