Republican presidential hopeful Rick Perry isn’t exactly a moderate, embracing a far-right line on just about every issue under the sun. Indeed, when his rivals question his “electability,” they’re referring to the limited appeal of such a very conservative candidate.

But there’s an exception, and apparently, it’s proving to be a doozy.

With a single phrase implying his opponents are heartless, Gov. Rick Perry of Texas plumbed a profound divide between his views on illegal immigration and those of many grass-roots conservatives, who up to now have been the core of his support for the Republican nomination.

Mr. Perry summoned the phrase in a debate on Thursday night to justify a Texas law that lets some children of illegal immigrants pay in-state tuition at public colleges. If you oppose it, he said, “I don’t think you have a heart.”

His remarks were instantly seized upon by rivals, none more so than Mitt Romney, who vetoed a similar bill as Massachusetts governor.

“I think if you’re opposed to illegal immigration, it doesn’t mean that you don’t have a heart,” he said Friday to a group of conservative activists. “It means that you have a heart and a brain.”

Perry’s rather sensible position on immigration generated hearty boos in Thursday night’s debate, and multiple reports from the straw poll in Florida yesterday mentioned GOP activists who started bailing on the governor after hearing his take on this issue.

Now, it’s worth noting that, in the 2008 race, John McCain was the lead Republican sponsor on comprehensive immigration reform and the DREAM Act — both of which the GOP base hate — and managed to win the party’s presidential nomination fairly easily anyway. The current race is quite a bit different, though, not only because the party is even more right wing now, but also because McCain shamelessly flip-flopped, abandoning his positions and denouncing the bills he helped write — while Perry is sticking to his guns.

When Romney and other Republicans attack on this issue — Perry backed a measure to allow children of undocumented immigrants to pay in-state tuition for higher education — they’re telling the truth. The best the Texas governor can do, at least so far, is to claim to have compassion, which only seems to enrage the GOP base even more, since it’s a line they’re accustomed to hearing from the left.

The result is the right-wing governor who thinks Social Security and Medicare are unconstitutional has been deemed too moderate because of a single issue conservatives care about.

If the Perry campaign were on top of its game, the response to this would be fairly obvious: at least Perry has been consistent, which is more than can be said about Romney, the one claiming the far-right high ground. After all, six years ago, Romney endorsed an immigration reform policy conservatives now consider “amnesty,” only to abandon that position after one of his many metamorphoses.

Why the Perry camp is proving to be so inept in punching back is a mystery.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.