It’s on! Ostensible allies for the last couple years, Sens. Ted Cruz (R-Texas) and Rand Paul (R-Ky.) have commenced the battle for the unofficial title of conservative front-runner. That’s no surprise, but what is remarkable is their choice of weapons: foreign policy. For the last several years, there has been a lot of overblown hype about how the GOP, particularly the party base, is becoming isolationist. So it’s interesting that Cruz would seek to get to Paul’s right on the issue.

The first round began in earnest less than 24 hours after Paul — to no one’s surprise — won the Conservative Political Action Conference straw poll by a country mile. (Ron and Rand Paul have always overperformed in such contests, and Rand has his father’s machine working for him.)

“I’m a big fan of Rand Paul. He and I are good friends. I don’t agree with him on foreign policy,” Cruz said on ABC’s “This Week.” ‘‘I think U.S. leadership is critical in the world, and I agree with him that we should be very reluctant to deploy military force abroad. But I think there is a vital role, just as Ronald Reagan did. . . The United States has a responsibility to defend our values.”

Paul responded almost immediately with an op-ed for Breitbart.com that was, depending on your reading, either a gentle rebuke or a not-so-passive-aggressive attack on Cruz. “Some politicians,” he wrote, “have used this time to beat their chest. What we don’t need right now is politicians who have never seen war talking tough for the sake of their political careers.”

Titled “Stop Warping Reagan’s Foreign Policy,” Paul’s op-ed is a clever bit of rhetorical jujitsu in which he criticizes others for using Reagan’s legacy while at the same time enlisting it for his own purposes. Paul offers a version of his father’s effort — during the 2008 and 2012 presidential primaries — to cast the Gipper as a noninterventionist who was plagued by hawks to his right.

Any analysis that casts the passionate anti-communist invader of Grenada (without congressional approval), supporter of the Contras and Afghan mujahideen, champion of missile defense, bomber of Libya and winner of the Cold War as a noninterventionist certainly gets points for creativity.

“I don’t claim to be the next Ronald Reagan nor do I attempt to disparage fellow Republicans as not being sufficiently Reaganesque,” Paul wrote, even as he disparaged politicians for distorting Reagan’s (allegedly) real record. “But I will remind anyone who thinks we will win elections by trashing previous Republican nominees or holding oneself out as some paragon in the mold of Reagan that splintering the party is not the route to victory.”

This last bit was a reference to Cruz’s CPAC speech in which Cruz mocked the GOP’s tendency to nominate moderates: “We all remember President Dole, President McCain and President Romney.”

While probably sincere, Paul’s long-standing commitment to Reagan’s 11th Commandment — “Thou shalt not speak ill of another Republican” — also serves as a shrewd attempt to inoculate himself against real vulnerability.

His father was an often vicious critic of his fellow Republicans, including Reagan. In 1987, Ron Paul left the GOP to run as a libertarian presidential candidate, in the process denouncing Reagan for “massive monetary inflation, indiscriminate military spending, an irrational and unconstitutional foreign policy, zooming foreign aid, the exaltation of international banking, and the attack on our personal liberties and privacy.” Reaganomics, said Paul the Elder, was simply “warmed-over Keynesianism.” Rand is a very different man than his father, but his big-tent conservatism is a bit ironic given the fact he worked on his father’s campaign and is the heir to the Paul machine.

I have no idea who will win this battle. Right now it’s hard to see how Cruz can get past Paul. It’s also hard to see how a mainstream media that unfairly turned Dole, McCain and Romney into extremists won’t make easy sport of Paul.

Last, it’s worth keeping in mind that no Republican since Reagan has won the nomination by first seeking to be the standard-bearer of the conservative base. That’s one aspect of the Reagan legacy both are eager to inherit.