Note: Lanny Davis is a volunteer with the Israel Project, an American nonprofit group that tries to get facts out about Israel to the media. This column represents his own personal views, not those of the Israel Project. — Ed.

Just suppose, hypothetically of course:

The people of Mexico elect as president a man who questions whether al Qaeda was behind the Sept. 11 attacks, who refuses to acknowledge that the United States has the right to exist and says it should be "wiped off the face of the earth," and who trains and funds anti-U.S. terrorists in Cuba and a Central American nation, who launch thousands of rockets and missiles into downtown Miami, New Orleans and Houston, killing Americans.

And suppose this Mexican president, backed by senior officials of his government, defies a U.N. Security Council resolution by continuing to develop enriched uranium that would give Mexico the ability to make an atomic bomb. And suppose, further, that there are grounds to fear that the Mexican president will secretly sell atomic bombs to anti-American terrorists he has funded or supported, including al Qaeda.

How would Americans react to such a threat? What would a U.S. government do under such circumstances?

Surely, at the very least, Americans would demand, and the U.S. government would agree to lead, a total economic embargo on Mexico, blocking all trade and financial transactions using the U.S. banking system and putting a freeze on all Mexican assets in the U.S.

And Americans would expect their government to exert maximum pressure on friends and allies and trading partners in Europe and Asia to do the same.

And, if the sanctions didn’t work, it is hard to imagine that the U.S. would not seriously consider taking military action to prevent Mexico, under this hypothetical scenario, from developing a nuclear weapon.

I have been very careful here in what may seem to be a far-fetched hypothetical. It certainly is far-fetched when it comes to our friendly neighbor to the south, Mexico, and I apologize for using it in the hypothetical to make my point.

But it is not far-fetched — it is stunningly, factually accurate — if you substitute the name Ahmadinejad for the Mexican president, Iran for Mexico, and Israel for America.

Iran's popularly elected President Mahmoud Ahmadinejad has questioned whether the Holocaust ever happened (though he has at times tried to take back his words after they were denounced throughout the world). Indeed, in public statements, he has asserted that there was a cover-up of the evidence concerning who was really behind Sept. 11, just as he claims there is an ongoing cover-up on whether there was a Holocaust.

The Iranian president, without any public repudiation by the highest leaders of the Iranian theocracy, including its Supreme Leader Ayatollah Ali Khamenei, has denied Israel's right to exist as a sovereign state and has said he favored "wiping Israel off the face of the earth." He and his government have indisputably funded and trained Hezbollah and Hamas, both of which have been branded internationally as terrorist organizations, and both of which have intentionally launched rockets to kill Israeli civilians.

And last week, the Financial Times reported that, in defiance of the U.N. Security Council resolution, Iran has reached a point in its nuclear enrichment program that allows it to create a nuclear bomb.

So now what is America to do about Iran's nuclear weapon program? And does anyone expect Israel to react any differently than America would if the above far-fetched hypothetical were actually true?

President Obama indicated during his campaign and since the election that his administration would be willing to engage in negotiations with Iran to improve relations with the U.S. and to convince it to stop its nuclear-bomb development program. I applaud him for that.

But in his first primetime press conference, on Feb. 9, Mr. Obama also said: "[Iran's] actions over many years now have been unhelpful. ... [Iran’s] financing terrorist organizations like Hezbollah and Hamas, the bellicose language that they've used toward Israel, their development of a nuclear weapon or their pursuit of a nuclear weapon create the possibility of destabilizing the region and are not only contrary to our interests but, I think, are contrary to the interests of international peace."

Mr. Obama and Secretary of State Hillary Rodham Clinton appear to be willing to use "carrots" and "sticks" to try to persuade Iran to abandon its effort to develop a nuclear bomb.

The "carrots" would be to offer improved economic and political relations with the U.S., aimed at appealing to what appears to be a significant middle class in Iran that is unhappy with its government and its daily lives, average Iranian families who prefer good relations with the U.S. and the West, including expanded trade, travel, improved education and cultural exchanges — in short, a better future for their children.

The "sticks" would be to institute and enforce much tighter economic sanctions — going so far as an absolute trade and financial embargo, including a ban on all U.S. company trade with Iran, a freeze on all Iranian financial assets deposited in this country and a block on all use of American banks and financial networks and systems.

Even though most of these sanctions were already on the books, they have often been ignored. As The Associated Press reported in the summer of 2008, U.S. exports to Iran grew more than tenfold during former President George W. Bush’s years in office, with household-name companies and major industries selling a variety of products to Iran, including military parts for F-16 fighter jets (!).

In the past, as far back as Jimmy Carter during the hostage crisis, America has been unable to persuade its European and Asian friends and allies to cooperate in also imposing these across-the-board sanctions, and thus, so far, they have failed to impose any real pain on Iran or be taken seriously within Iran.

Perhaps the best way for the world to understand the true danger of a nuclear Iran is to recognize that the threat goes far beyond Israel's true existential threat.

It's still a little-known fact that there is great hostility towards Iran and fear of its developing a nuclear bomb from Sunni-dominated Arab governments in the Middle East. This is not only religiously based, given centuries of hostility and warfare between the Shiites who dominate Iran versus the Sunnis who prevail in most of the rest of the Middle Eastern Arab nations. It is also based on long memories by Arabs going back several thousand years, when the Persian empire occupied and abused Arab peoples.

It is increasingly obvious that such Sunni Arab nations as Saudi Arabia, Egypt and Jordan cannot afford to allow Iran to go nuclear without trying to do so themselves. There is also reportedly genuine fear that Arab states in close proximity to a nuclear weapon-possessing Iran, such as Syria, Iraq and the Persian Gulf states, would feel pressure to cut deals with a nuclear-bomb-possessing Iran at the expense of Western interests.

But what if the economic sanctions fail? The military option will not be easy. Iran’s nuclear enrichment facilities are reportedly buried under thousands of feet of concrete- and steel-protected laboratories spread out in many different locations throughout the nation. (At least, that is what Iran would like the world to think — perhaps just as Saddam Hussein wanted the world to think that he had WMDs?)

Therefore, air power alone may not be enough.

But that does not mean that the Iranian government and the Iranians who elected Ahmadinejad president can assume that the world, the U.S. and especially Israel can afford to sit idly by while Iran develops the capability to build a nuclear bomb. If there is no choice, there could well be a military option exercised, which at the very least could do damage to Iran’s nuclear progress, slow it down and be a signal of more to come unless Iran reverses its policy.

If the Libyan dictator Col. Moammar Gadhafi got the message from U.S. military strikes and decided to abandon his nuclear bomb program in favor of the "carrots" of U.S. and Western economic aid and trade, perhaps the Supreme Leader of Iran and Iranian voters will get the message and oust the extremist Holocaust-denier and Israel-hater who is their president.

In the final analysis, this issue may be the greatest challenge facing the Obama administration. If there are two people who can find the right balance to communicate to Iran's leaders between "carrots" and "sticks," it is Mr. Obama and the brilliant and capable Mrs. Clinton.

Let's hope Iran's Supreme Leader and Council take Mr. Obama and Mrs. Clinton up on their invitation to unclench Iranian fists and reach out to shake the American leaders' open hands.

This article appeared in Mr. Davis's weekly column, "Purple Nation," in The Washington Times on Monday, Feb. 23.