Today in Kentucky, Republican primary voters are poised to hand a major defeat to the GOP establishment and the neoconservatives (if the two can be distinguished). Rand Paul, a Bowling Green ophthalmologist and the son of Rep. Ron Paul, R‑Texas, has a healthy lead over Old Guard favorite Trey Grayson in the nomination contest for the 2011 Senate race.

Should Paul win that seat, it could open the door to fresh thinking in the GOP on foreign policy and the war on drugs.

The Tea Partiers who back Paul the Younger often carry signs like “Ayn Rand Was Right.” Given father Ron’s libertarian convictions, people often assume that Rand Paul is named after the self‐​styled “radical for capitalism” who wrote Atlas Shrugged.

Actually, “Rand” is short for “Randall” — though “Trey Grayson” sounds like a moniker Miss Rand might have given to one of her lesser villains, a “timeserver,” rather than a menacing arch-“looter.”

Establishment hawks see the race as an epic battle, however. Grayson’s garnered endorsements from the likes of Rudy Giuliani and Dick Cheney, who fear that a Paul victory would be read as a repudiation of neoconservative foreign policy.

Rand has distanced himself from his father’s foreign‐​policy noninterventionism, insisting he’s for the war in Afghanistan and against rapid withdrawal from Iraq. That hasn’t stopped Trey the Gray’s backers from trying to make the campaign a referendum on Rand Paul’s allegedly “strange ideas.” They may be sorry they did.

“Paul would’ve Voted Against the War in Iraq,” crows a Grayson campaign Web site, rand​paulstrangei​deas​.com. Yes, that must seem strange indeed to the American public, over 60 percent of which routinely tells pollsters that they’re against the war.

Stranger still to establishment Republicans apparently, is the fact that “Paul Criticized the Gonzalez [sic] v. Raich Decision” on medical marijuana.

If the Grayson team knew the first thing about that 2005 Supreme Court case, they’d know it’s a major obstacle to battling Obamacare. Raich upheld the feds’ power to prosecute medical marijuana patients on the theory that even those who grew and consumed their own crop were engaged in interstate commerce.

As Justice Clarence Thomas’ dissent pointed out, that means Congress “can regulate virtually anything,” even “quilting bees and potluck suppers.” Obamacare’s defenders are delighted they’ll have that precedent available when the individual mandate reaches the court.

Rand, a more cautious politician than his dad, has dodged these attacks deftly. Father Ron’s success owes largely to what you might call a “cult of no personality.” I mean that in a good way — the Texas congressman, who’s given to earnest lectures on the Constitution, lacks the artful charm of the professional pol. In an age of prepackaged sound bites, many find Rep. Paul’s guilelessness electrifying.

Paul 2.0 is more circumspect: Rather than openly advocate drug decriminalization, Rand favors “a more local approach to drugs … it’s a state issue.” He sells foreign‐​policy restraint pragmatically, “oppos[ing] reckless ‘nation building’ or burdening our troops by making them the world’s police force.”

Those positions aren’t nearly as unpopular as party dinosaurs would like. Support for marijuana legalization is growing, and, in a 2007 poll, 76 percent of Americans agreed “the U.S. is playing the role of world policeman more than it should be.”

In a March forum at the Cato Institute, Rep. Tom McClintock, R‑Calif., suggested that a silent majority, “more than half of the Republican caucus,” has serious doubts about the approach to foreign policy that dominated the Bush years. If a noninterventionist — even one half in the closet, like Rand Paul — wins over Republican voters, that could embolden other freethinkers — a healthy thing for the party and the country.