President Barack Obama has decided to test whether Iranian President Hassan Rouhani’s “charm offensive” is a legitimate effort to reach an agreement on a more constricted and transparent Iranian nuclear program. With this decision, he embarks on the most transformative and important diplomatic initiative of his presidency.

The closest historical analogy is President Richard M. Nixon’s opening to China in 1971. Nixon had recognized a major adversary’s new willingness to change course and he seized the opportunity to further vital U.S. national security interests.

This China analogy, however, has some flaws. Most important, Nixon and his national security adviser Henry A. Kissinger began their quest in secrecy to avoid a divisive public debate that could have scuttled the initiative. Obama’s public commitment to test an opening to Iran, though, will be subjected to fierce scrutiny by domestic and foreign opponents.

But other historic analogies now being suggested do not work at all. The much cited Munich analogy of “appeasement” of Adolf Hitler on the eve of World War Two is absurd, since Iran’s Supreme Leader has neither the stated objective, nor the capability to take over the Middle East. Iran also has no history of military expansionism.

Nor is Rouhani Iran’s version of Mikhail Gorbachev, as some have suggested. Rouhani’s objective is to strengthen Iran’s governing system, not to “restructure” it, after the crippling eight years of the Ahmadinejad regime. He is working for a Supreme Leader who is determined to hold on to power and to strengthen the Islamic Revolution.