As gung-ho "experts" press President Obama to do this, that or the other in the Middle East, keep a simple rule in mind: Whatever the avid interventionists suggest probably won't work -- and surely will have unintended consequences.

Obama's overall policy toward the region has been modest, cautious, incremental and situational. His boldest move has been to try negotiations, rather than airstrikes or stronger sanctions, as a way to constrain Iran's nuclear ambitions. He has been reluctant to commit U.S. military forces and hesitant to enforce red lines, even his own. He has eschewed unilateralism, pressing allies to do their part.

Critics look at the bloody instability throughout the region and charge that Obama has been passive. But history suggests that more active U.S. involvement would likely make things bloodier.

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A case in point is the conflict in Yemen, where a coalition led by Saudi Arabia has launched extensive airstrikes to bolster the recognized government against Houthi rebels who threaten to take over the country.

On one level, the fighting amounts to a proxy war between two would-be regional superpowers -- Saudi Arabia vs. Iran, which supports the Houthis. On another level, Yemen is but one battlefield in a wider religious war, Sunni against Shiite, that is playing out across the region. On yet another level, the fight is personal: Ali Abdullah Saleh, the longtime dictator who was deposed during the Arab Spring, has allied himself with the Houthis in an apparent attempt at a comeback.

Saleh, who is Shiite, violently repressed the Houthis while he was in power. He was seen as a crucial U.S. ally in the fight against al-Qaeda, which has a more active and menacing presence in Yemen than perhaps anywhere else in the world. So, to all those who complain that Obama has kept the United States on the sidelines when we ought to be doing something, the question is: precisely what?

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Should Obama intervene forcefully on behalf of Saleh's successor, Abed Rabbo Mansour Hadi, who had to flee the country by ship as Houthis threatened to capture the port city of Aden? If so, we would be fighting against the Yemeni faction that most implacably opposes al-Qaeda, which remains determined to stage attacks in the United States.

In the Middle East, it has been said, "the enemy of my enemy is also my enemy." This seems to be the case in Yemen, where the U.S. goal, surely, is to strengthen neither the Iranian-backed Houthis nor al-Qaeda. It is difficult to see how decisive intervention on either side would serve our national interest or make us safer. And it is easy to imagine how we could unintentionally make the situation much worse.

After all, we've consistently done just that. The 2003 invasion of Iraq was intended to implant a multiethnic, multicultural democracy at the very heart of the Muslim world. Instead, by destroying every vestige of the secular Iraqi state -- unspeakably brutal though it was -- the United States ended up allowing long-smoldering tensions between Sunnis and Shiites to ignite. The U.S.-sponsored government in Baghdad turned out to be a brigade of arsonists, not firefighters. As a result, the United States is now allied with Iran (though neither country wishes to admit it) in an attempt to keep Islamic State militants from capturing the Mesopotamian heartland.

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Small wonder, then, that Obama has turned a deaf ear to those advocating some kind of robust intervention in Syria. When aides pressed him to arm the "moderate" Syrian rebels, he demanded convincing evidence that U.S.-supplied weapons would not soon end up in the hands of unambiguous enemies. The battlefield success of well-trained Islamic State fighters suggests that Obama's caution was well-placed.

Current U.S. military action against the Islamic State -- lots of airstrikes in Iraq, much less focus on Syria -- has the effect of strengthening the regime of dictator Bashar al-Assad in Damascus. This is the same Assad who crossed Obama's "red line" by using chemical weapons against his people. It's the same Assad who, Obama once declared, had to go.

Is it inconsistent, then, to pursue policies that help keep him in power? Yes, but it is probably also wise, at least for now. If the Assad government were to disappear tomorrow, it would likely be replaced by something more volatile and more threatening to U.S. interests.

The upheaval taking place across the Middle East is unprecedented. I don't know if U.S. intervention can make things better. But I know it can definitely make things worse.
    
Eugene Robinson's email address is eugenerobinson@washpost.com.