Why did Sarah Palin reject an invitation to deliver the keynote address to the crowd gathered this weekend for the annual Conservative Political Action Conference, arguably the most prime of prime speaking gigs on offer to potential 2012 Republican presidential contenders?

The GOP’s 2008 vice presidential nominee surprised more than a few conservative activists and political pundits when she turned down the speaking invite for the annual gathering of right- and righter-wingers, which finishes this weekend in Washington. Palin says she’s got family obligations, even though those obligations have rarely prevented her from jetting off to the paying gigs that have made her a very wealthy woman.

So what gives? The fact is that CPAC crowd, which is very serious about its conservatism, has never been as bedazzled by Palin as the pundit class. Outgoing American Conservative Union chair David Keene, the former Reagan aide who has been the player in the development of the conference as a major GOP venue, has never been too keen on Palin. After she quit the governorship of Alaska at midterm, he said: “You’ve got to be more than a rock star. If in fact she’s interested in the presidency, she has got to establish herself as someone you can envision in the Oval Office. And it’s become more difficult to envision than it was at the time of the election.”

But Keene, one of the most experienced tacticians on the right, would never let disappointment with a particular political player’s decision get in the way of pumping up CPAC. So the invite went out to Palin. She, above all other ambitious Republican pols, was offered the most coveted of speaking slots.

Still, the answer was “no.”

Why?

A conservative rival, who is busily positioning for a presidential bid, was quick to suggest that the real reason Palin’s skipping CPAC is because its not one of those paying gigs that the former governor always seems to be able to fit into her schedule.

“I have a feeling she has some demands on her time, and a lot of them have financial benefit attached to them,” snipes former Pennsylvania Senator Rick Santorum.

While Santorum acknowledges that cashing in on her fame might pay benefits to the Palin family—in the form of a bigger balance in the household account—he slyly suggested that he was more interested in advancing the conservative cause than money-making “opportunities.”

“I don’t have other responsibilities like she has, other opportunities like she has—like I said, other business opportunities that may be in conflict with what she was asked to do,” explains Santorum.

That drew a classic “Mama Grizzly” lashing from Palin, the most vengeful Republican since Richard Nixon.

The politician-turned-media phenomenon seemed to suggest that while she is not a feminist, Santorum is a sexist. From one of her many paying gigs—Fox commentator—Palin surmised that, were the senator to look in the mirror, he might see the reflection of a “knuckle-dragging Neanderthal.”

True enough, on so many levels.

As it happens, Santorum has made some of his own “family obligations” excuses over the years—for instance, when he claimed a Pennsylvania residence for his five children (who lived in Virginia) in order to avoid paying $100,000 in cyber-education tuition fees.

But, for all his flaws, Santorum’s jab at Palin is about more than pettiness.

It illustrates the growing tension within the GOP regarding the former governor of Alaska, a genuine celebrity on the right who savvy activists have begun to note always seems to takes more from the conservative movement than she gives back. What she is taking now, of course, is the energy that might be directed toward another right-wing candidate for the 2012 GOP nod—someone like, say, Rick Santorum.

Palin may not run for president. Indeed, there is plenty of evidence to suggest that her only real backers are the naïve Tea Partisans who buy whatever product—or line—she’s peddling and Democratic strategists, who delight in the polling data that shows President Obama could beat the Alaskan even in bright red Southern states.

Still, the time between now and the moment when she announces that “family obligations” or “business opportunities” will prevent her from running is the time when other conservatives could be positioning to win the nomination.

That’s creating anxiety, and nastiness, on the right.

What distinguishes Santorum is not the fact that he entertains doubts about Palin’s seriousness and sincerity. What distinguishes him is his willingness to take a public poke at Palin.