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It has become conventional wisdom that the roller coaster of American decision-making on the Syria issue has dealt a significant, if not mortal blow, to American credibility and leadership in the world.

This perception is not without good reason.

When President Obama first established a "red line" in Syria on their use of chemical weapons, it was seen as a way to avoid or postpone any decision on U.S. intervention on the side of the rebels against the authoritarian regime of Bashar al-Assad.

Then, after the chemical attack that left many dead, and the president’s commitment to military action in response, his sudden turnabout in going to Congress raised further questions.

Then followed a third twist in the road, with a difficult congressional vote looming, when the president announced qualified support for a Russian proposal to monitor, control and eventually dismantle the Syrian chemical store.

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All of which left many people questioning the administration’s ability to be taken seriously as a leader on many global challenges.

The ultimate test of this proposition, however, will not be on the Syrian matter, as important as it is, but on the Iran nuclear challenge.

While there is already much speculation concerning the impact on Iran of witnessing this American flip-flopping and uncertainty, there are things that the administration can do going forward to restore belief that America’s word is sacrosanct and that it is capable and willing to make tough decisions and take bold action when necessary.

It starts with the administration’s case that the Russian initiative on Syrian chemical weapons would never have surfaced in the first place and would never reach a satisfactory conclusion without the threat of U.S. military action.

This theme now needs reinforcement regarding Iran.

Despite all the talk of a more moderate Iran under the new president, Hassan Rohani, there is no tangible indication of any Iranian give on the nuclear issue. And Rohani himself said the other day that his government would not cede its “absolute right” on what he called “the nuclear issue.”

The U.S., therefore, needs to reiterate in even stronger terms than heretofore that the military option is not only still on the table but becomes more relevant the longer Iran stalls and the more it continues to enrich uranium and moves on a second front toward a plutonium bomb.

To those who would doubt the seriousness of such statements after the Syrian affair, several things need to be addressed by the administration:

First, the reason for bringing the Syrian issue to Congress -- the absence of a direct threat to the U.S. -- does not apply to Iran. In the case of Iran, unlike Syria, the development of a nuclear capability is a direct strategic threat to the United States and to its interests and values throughout the Middle East.

If the U.S. sees Iran reaching a point of no return on the nuclear matter, the administration will have to act, on its own if necessary.

Second, for those who would want to avoid a military confrontation with Iran, the best chance lies in making clear that continued Iranian obstinacy will inevitably lead in that direction.

Why should Iran believe in that threat after Syria? For several reasons:

• First, if the Russian initiative on Syrian chemical weapons does not work out the likelihood remains that the U.S. will attack after all.

• Second, simply because the implications of Iran having a nuclear weapon are so dramatic vis-à-vis security in the Middle East, the sustainability of the flow of oil, the threat to Israel, Saudi Arabia, the United Arab Emirates and others in the region, as well as the realization that extremist regimes such as that of Iran might actually use weapons of mass destruction however irrational such action may seem (think Syria using chemical weapons as U.N. inspectors were on the ground).

• Finally, the U.S. will now be aware of claims of a credibility and leadership gap and will be more eager to disprove the notion that the era of American global leadership was over, particularly in a case where the word of the president to prevent Iran from going nuclear has been a hallmark of his tenure.

There is no doubt that American credibility has been hurt. This is bad for the world and bad for America. As Robert Kagan has written, despite all kinds of criticism of American foreign policy, the world would be a far worse place if America was not there to lead.

The harm caused by American ambiguity on Syria can be undone.

Iran is the real opportunity to make things right once again. Iran is where American strength and leadership are crucial.