But Sullivan argued in his endorsement that his unconventional politics were emblematic of a changing political culture.

"I am, like many others these days, politically homeless," Sullivan writes. "A moderate, restrained limited government conservatism that seeks to amend, not to revolt, to reform, not to revolutionize, is unavailable."

And while Sullivan says he does not support "many of his nuttier policy proposals," he sees Paul's libertarianism an important counterweight in conservative politics.

"Breaking the grip of neoconservative belligerence on conservative thought and the Republican party could make space again for more reasoned and seasoned managers of foreign policy," Sullivan writes. "Embracing the diversity of a multi-cultural, multi-faith America is incompatible with Christianism and the ugly anti-illegal immigrant fervor among the Republican base. But it is perfectly compatible with a modest, humble libertarianism that allows a society to find its own way, without constant meddling and intervention in people's lives."

Paul is running second in a PPP poll of likely Iowa caucusgoers released Tuesday, just one percentage point behind leader Newt Gingrich.