Senator Rand Paul (R–KY) yesterday gave a thought-provoking speech on foreign policy at The Heritage Foundation in which he argued that “a more restrained foreign policy is the true conservative foreign policy, as it includes two basic tenets of true conservatism: respect for the constitution and fiscal discipline.”

He compared the “relentless force” of radical Islam with the threat posed by communism during the Cold War and called for a “firm and patient” containment policy based on economic pressure, deterrence, and diplomacy, with the use of military force considered only as a last resort.

Although few conservatives would disagree with that prescription, he rightly raised concerns about Iran and argued that there might be policy options between trying to talk to Iranian President Mahmoud Ahmadinejad to death and bombing Iran. He suggested the U.S. consider a version of a strategy of containment. Heritage examined this option in previous research. The containment option carries with it serious concerns.

First, the United States has had a mixed record of containing a non-nuclear Iran, and this will only get much more difficult and dangerous after Iran has acquired a nuclear weapon. Iran has already ordered terrorist attacks against Americans in Lebanon, Saudi Arabia, Iraq, and Afghanistan as well as Saudi and Israeli diplomats in Washington, D.C. It is likely that a nuclear Iran would become even more aggressive in its support of terrorism.

Unlike the Soviet Union—which was imbued by an ideology that predicted the inevitable victory of communism and patiently prescribed constant evaluation of the correlation of forces before setting foreign policy—Iran’s Islamist regime espouses an ideology that extols martyrdom and demands implacable resistance to the “satanic” power of the U.S., which is denigrated as the chief barrier to implementing God’s will on earth.

Moreover, Ahmadinejad and other leaders in Tehran advocate an apocalyptic doctrine that recognizes a need to hasten the return of the Hidden Imam as the Mahdi (“Guided One”) who will defeat the forces of evil in a final battle. The danger is that this religious fanaticism may lead Tehran to provoke conflict to accelerate the coming of the Mahdi.

Second, a nuclear Iran would be difficult to deter. As Middle East scholar Bernard Lewis has noted: “With these people in Iran, mutually assured destruction is not a deterrent factor, but rather an inducement.”

Third, containing a nuclear Iran would require close alliances with Iran’s neighbors and a beefed-up U.S. military presence in the Persian Gulf. This would require a costly long-term military, economic, and political commitment that Senator Paul has argued against elsewhere.

Fourth, containing a nuclear Iran would be extremely dangerous. It would require a willingness to use military force in defense of U.S. national interests and those of our allies. As bad as a preventive war with Iran could be, war with a nuclear Iran would be much worse.

Finally, allowing Tehran to gain a nuclear weapon would trigger a cascade of nuclear proliferation by countries threatened by Iran, such as Turkey, Saudi Arabia, and Egypt. This would make the volatile Middle East even more dangerous.