What a way for the Iranian Revolutionary Guard to welcome President Bush to the Middle East — by dispatching five high-speed boats to threaten three American Navy vessels in the Strait of Hormuz with a radio transmission warning of explosions and with what an American admiral, Kevin J. Cosgriff, described as “white box-like objects that floated.”

It is a reminder that the nuclear weapons program that the American National Intelligence Estimate claims was suspended is hardly the only way that Iran threatens American, or Western, interests. There are conventional threats, as well, such as the Iranian navy. Iran’s biological and chemical weapons programs also bear mentioning, as does its support for terrorist organizations including Hezbollah, Hamas, and Al Qaeda.

The Iranians were no doubt emboldened by the feeble British reaction to the seizure last year of 15 Royal Navy personnel. After returning the sailors, Iran suffered no consequences for its action. So why not try an attack on the American Navy?

Mr. Bush, with more than a year left in his presidency, is no lame duck. He is experienced and wise enough to respond to the Iranian provocation at a time and place of his own choosing. The important thing is less the timing than the message that there will be a response, for if the Iranian challenge goes unresponded to, it only increases the risk that the next Iranian raid on American troops or on an American city will be a deadly one.