In an illuminating essay for National Journal, Michael Gerson writes about the foreign-policy debate roiling the GOP. Going back to Dwight Eisenhower’s victory over Robert Taft in 1952, Gerson points out that since that moment the GOP has been an internationalist party.

There have been differences for sure–most notably Ronald Reagan’s challenge of Richard Nixon and Henry Kissinger’s policy of détente, with Reagan embracing the roll-back of the Soviet empire–but they have all been differences among internationalists. Mr. Gerson argues that the rise of Kentucky Senator Rand Paul represents an effort by non-interventionists to remake the core national-security doctrine of the GOP. Gerson quotes George Mason Professor Colin Deuck, who says of Paul’s approach: “This is not just a rejection of Bush 43. It goes way beyond Reagan versus Nixon. It is an attempt to undo the Eisenhower administration, which locked Republicans into an internationalist stance.”

Mr. Gerson highlights Senator Paul’s positions on various national-security issues:

The talented, ambitious Republican senator, with little background in foreign affairs, has proposed defense cuts, opposed the “perpetual war” against terrorism, questioned American troop deployments in Germany and South Korea, and sought to limit presidential authority over the use of force (urging, for example, the congressional deauthorization of the Iraq and Afghan wars)… Paul has systematically opposed the forward deployment of American influence: drone strikes, military engagement, and foreign assistance (which, he argues, encourages “lethargy” and “insolence”). Paul’s “constitutional foreign policy” denies the legal basis of the war on terrorism, would place severe constraints on the executive, and hints at the existence of an oppressive national security state.

The political and policy atmosphere of 2013—conflict fatigue, the Arab’s Spring’s frightening turn, public concerns about drone policy, revelations about NSA spying—could hardly have been more favorable to Rand Paul’s rise. It is particularly revealing what a leader says when he is on top of the world. During his 12-hour, 52-minute drone filibuster, Paul felt enough support and permission to make extraordinary claims about the potential misuse of presidential power. “That Americans could be killed in a café in San Francisco,” he said, “or in a restaurant in Houston or at their home in Bowling Green, Kentucky, is an abomination.”

This was the perfect melding of domestic and foreign policy libertarianism—an assertion that the national security state might not only violate your privacy but also take your life during lunch. It was also a paranoid delusion. Taken as a serious argument, it would mean that the president of the United States can’t be trusted with advanced weaponry.

Senator Paul understands that his libertarian convictions are still out of step with many in the GOP, which is why he’s careful in how much he reveals, careful in the battles he chooses, and why he insists his views are Reaganesque (his latest effort can be found in his op-ed in today’s Wall Street Journal).

Having worked in the Reagan administration and having read a great deal about Reagan and his presidency, it is risible for Paul to claim his philosophy mirrors Reagan’s. America’s fortieth president, among other things, was not drawn to bizarre conspiracies, which Paul can be. (For example, Paul accused Vice President Cheney of being in favor of the Iraq war because of his ties to Halliburton and warns that the NSA might soon “start using the GPS feature in your phone to track whether or not you go to gun shows.”) Rand Paul’s philosophy is much closer to his father Ron Paul’s than Reagan’s or, for that matter, Eisenhower’s.

Senator Paul, then, does not represent simply a different point on the GOP’s post-World War II foreign-policy continuum. He is a break from that tradition. Whether that is wise or not is open to debate. But Mr. Paul should at least have the courage of his libertarian convictions. Particularly if he decides to run for president in 2016, Paul should level with us about how radically different his foreign policy as president would be from those of the last six Republican presidents.