Remember President Barack Obama's first major address abroad? It was in June 2009 at Cairo University, when U.S. ties with the Muslim world were in serious need of repair. If any American leader could help engineer a course correction, it was Barack Hussein Obama. The president told his audience: "I've come here to Cairo to seek a new beginning between the United States and Muslims around the world, one based on mutual interest and mutual respect."

It was a great speech, one of Obama's best. In a way, it was Obama's version of Martin Luther King's "I have a dream" speech, keyed to U.S.-Muslim relations rather than race relations in the United States. Unfortunately, the president's hopes have been dashed by events well beyond Washington's ability to shape, let alone control, the Muslim world. Egypt is a mess, Syria is in a far worse condition, and the problems are spreading.

But Syria is actually more of a heartbreaking distraction. The real prize in this part of the Muslim world would be to reach an accord with Tehran that constrains Iran's nuclear program by placing continuous, intrusive monitoring on known nuclear facilities, permitting inspections of suspected sites and removing quantities of enriched material from the country. In return, sanctions would be rolled back, and Tehran would be permitted to continue low-level uranium enrichment.

The Israeli government, some of its supporters in the United States and powerful Iranian interests would not be pleased with the parameters of this deal. But if Obama has his eyes on this prize, he has to be willing to absorb heavy punishment and defend his handiwork with the tenacity of a 1960s civil rights leader.

This assumes, of course, that Iran's new president, Hassan Rouhani, also has his eyes on the prize -- in his case, the revival of Iran's economy and its reintegration into the international community. Even if Obama and Rouhani are able to succeed, the Syrian detour could lead them far astray.

U.S. military strikes in Syria cannot be justified under the rubric of a responsibility to protect the Syrian people, because more than 100,000 have already died from other causes during the Syrian civil war. The case for U.S. military action therefore rests on the defense of an international norm against using chemical weapons and the defense of Obama's credibility, which will matter more in dealings with Tehran than in dealings with Damascus.

Obama has framed this as a national security imperative, as he must. But credibility and national security are inextricably linked. When presidential threats and red lines are devoid of consequence, Washington's standing and leverage diminish everywhere. If Congress refuses to authorize cruise missile strikes at this juncture -- when the president has no intent on putting boots on the ground and when evidence of the Syrian government's use of chemical weapons is overwhelming -- the damage to U.S. foreign and national security policy will be immense.

The ironies of this procession of events rebuke logic. Washington punished itself more than its adversaries by waging two ill-planned wars in Afghanistan and Iraq -- the latter based on false premises and faulty intelligence. And now the American public and its elected representatives are being asked to support yet another, albeit limited, use of force to uphold an international norm and U.S. credibility.

Employing cruise missile strikes to uphold an international norm against using heinous weapons makes sense if other leaders are inclined to follow Syrian President Bashar Assad's example. But Assad's conduct has been so reprehensible that other strongmen, no matter how evil, would pause before using chemical weapons.

The case for a limited retaliatory strike lies elsewhere, on Washington's credibility and standing, especially in dealing with the new Iranian government. Here, too, the pitfalls are obvious, even if they are not completely evident at this juncture. American credibility will be further diminished if Syrian forces continue to use chemical weapons after cruise missile strikes, thereby forcing a presidential choice of repeated air strikes or retrenchment. And cruise missile strikes could well provide spoilers with new opportunities to block a nuclear deal with Iran.

The decision to authorize the use of force in Syria is profoundly different than the second Iraq War. President George W. Bush wished to engage in a land war in the Middle East and the U.S. intelligence community obliged him by not exercising due diligence. President Obama wishes to punish Assad and his military in a limited way, without putting boots on the ground. Plentiful intelligence provides support for the limited use of force, and this president will avoid another land war in the Middle East.

If Congress rebukes the president, employing the same disingenuous and feckless arguments heard in the British House of Commons effectively preventing Great Britain from joining in a strike against the Assad regime, the prize of containing the Iranian nuclear program will become more remote.

Obama has yet to signal a readiness to accept the challenge of a negotiated settlement with Tehran. Now events in Syria have made this climb even steeper. If the president uses military force in Syria and does not actively seek a negotiated settlement of the Iranian nuclear program, this use of force will be unwise.

Obama and Congress face a world of poisonous choices. They cannot control events in Syria, where the president has unwisely put U.S. credibility on the line. The question at hand is whether standing down in Syria will cause more damage to American interests than the execution of limited strikes for limited purposes. Standing down without compensatory steps by the Assad regime will have greater poisonous consequences than limited strikes.

Michael Krepon is co-founder of the Stimson Center and author of "Better Safe than Sorry: The Ironies of Living with the Bomb."