Dick Cheney has broken former-veep protocol by elbowing an endorsement into the May 18 GOP Kentucky Senate primary between Secretary of State Trey Grayson and Dr. Rand Paul, son of Texas Congressman and presidential hopeful Ron Paul. Indeed, Paul so offends Cheney that the ex–VP hasn’t merely blessed Grayson (a former Democrat) as the "true conservative"; he’s attacking Paul, a first-time candidate who opened up a lead in the polls early in the campaign, with the sort of language usually reserved for trashing liberal Democrats. "We need senators who truly understand [radical Islam and Al Qaeda] and who will work to strengthen our commitment to a strong national defense and to whom this is not just a political game," gripes Cheney. As if his crabbing weren’t enough, former New York Mayor Rudy Giuliani is slamming Paul with equal force.

Why is Cheney so upset about a candidate who opposes taxes and spending, is a favorite of the tea party right and even sports a Sarah Palin endorsement? For one thing, Paul is his father’s son. Ron Paul’s old-right Republicanism, with its disdain for military intervention—including the war in Iraq—and taste for civil liberties, never sat well with the GOP’s foreign-policy establishment, as the nasty wrangling between the Congressman and Giuliani during 2007 debates illustrated. The neocons fretted when the elder Paul’s presidential bid claimed the national spotlight partly by calling into question their carefully constructed fantasy that only liberal "surrender monkeys" oppose unnecessary wars. Now they’re even more worried by the prospect that a GOP senator might apply checks and balances to presidential warmaking.

Rand Paul says, "I would have voted no on the Iraq War." He also says, in a video posted prominently on his campaign website, that he’ll push for formal declarations, with House and Senate votes, before the launch even of wars he might favor. He says that while national defense is the top responsibility of government, conservatives who are serious about reducing waste must be wary of the excesses of the military-industrial complex. Add on criticisms of the Patriot Act and a willingness to cross partisan lines, and you can see why Rand Paul gets Cheney’s goat.

What really troubles Cheney and his circle, according to the Cato Institute’s David Boaz, is the prospect that a Paul win would begin to crack the false facade of party unity on military intervention. "That’s an issue the GOP establishment doesn’t want an open debate on," says Boaz, who suggests the neocons "desperately fear that [electing] a conservative anti-interventionist leader on foreign policy just might reveal that a lot of Republicans and conservatives…don’t buy the world-policeman foreign policy the Bush/Cheney administration imposed on the GOP."

Paul could be joined on this fall’s list of GOP Senate candidates by another dissenter from neocon dogma. Former California Representative Tom Campbell is the front-runner in that state’s June primary, despite taking a battering from his chief foe, former Hewlett-Packard executive Carly Fiorina, because he once mounted an academic-freedom defense of then–University of South Florida professor Sami Al-Arian, who was under attack for promoting Palestinian causes. More of a libertarian, especially on social issues, than Rand Paul, Campbell is a fiscal hawk who takes plenty of traditionally conservative stands. But he also sports a Congressional record of opposing Bill Clinton’s Kosovo war, an opposition that included joining liberal Democrats in a bipartisan lawsuit that sought to have the undeclared military adventure ruled unconstitutional. He started calling for the withdrawal of US troops from Iraq in 2004, although he has been supportive of the Afghanistan occupation. These days, Campbell says, "There are…occasions when the United States should decline the invitation to go to war. This is especially so where United States interests are not directly at risk, or where success will depend upon many years’ involvement in nation-building."

That’s hardly a radical line, but it is radically at odds with the neoconservative worldview. To be sure, even if Rand Paul and Tom Campbell eventually make it to the Senate, there will still be plenty of Republicans who want to play world policeman. But even progressives with concerns about domestic policies advanced by a Paul or a Campbell will appreciate the irony in Senator Russ Feingold finally having some GOP Senate allies when he questions why America has not formally declared a war since the 1940s, and when he says Congress should apply constitutional checks and balances on imperial presidents. And, of course, there’s the richer irony that Republican primary voters might upset the best-laid plans of Dick Cheney.