Last May, U.S. Vice President Joe Biden took an extremely hard line on Iran. ”We will prevent Iran from acquiring a nuclear weapon by whatever means we need,” he said.

This week Defense Secretary Leon Panetta said the same thing. “We will not allow Iran to develop a nuclear weapon,” he said on Sunday. He followed that up in Jerusalem with something even tougher: “I want to reassert again the position of the United States that with regard to Iran, we will not allow Iran to develop a nuclear weapon, period. We will not allow them to develop a nuclear weapon, and we will exert all options in the effort to ensure that that does not happen.”

What’s missing is anything like these words from President Barack Obama. He has been far less specific. “As president of the United States, I don’t bluff,” he said in March. “I also don’t, as a matter of sound policy, go around advertising exactly what our intentions are. But I think both the Iranian and the Israeli governments recognize that, when the United States says it is unacceptable for Iran to have a nuclear weapon, we mean what we say.”

Speaking to AIPAC that month, he said: “I have said that when it comes to preventing Iran from obtaining a nuclear weapon, I will take no options off the table, and I mean what I say. That includes all elements of American power: a political effort aimed at isolating Iran, a diplomatic effort to sustain our coalition and ensure that the Iranian program is monitored, an economic effort that imposes crippling sanctions and, yes, a military effort to be prepared for any contingency. Iran’s leaders should understand that I do not have a policy of containment; I have a policy to prevent Iran from obtaining a nuclear weapon. And as I have made clear time and again during the course of my presidency, I will not hesitate to use force when it is necessary to defend the United States and its interests.”

But saying “I do not bluff” or “I have a policy” is not the same as saying what Panetta said. That the president has never said words as tough as those of his subordinates must alarm the Israelis, for they know that the only view that counts is Obama’s. It is sometimes argued in his defense that he wants to leave options open and avoid specificity, but that’s just the problem. He should “advertise what our intentions are.” Why could he not say what Panetta just did? If the goal is to confront the ayatollahs with a stark choice, why not make it starker?

That Obama fails to do so may produce in both Jerusalem and Tehran uncertainty as to whether, in the end, he will use force to prevent an Iranian nuclear weapon. If his diplomatic and economic efforts against Tehran are to have the slightest chance of success, and if his efforts to persuade Israel not to strike Iran are to succeed, that uncertainty must be eliminated. Only if Obama can fully persuade the Ayatollah Khamenei that Iran will never get a nuclear weapon, that all the effort and isolation and expense have been wasted, and that the goal will never be achieved because the American military will block it, is there any chance that Iran will change course. The very clear statements by the secretary of defense only underline the absence of equal clarity from the commander in chief.