As perilous and as flawed as it may be, Congress and the public should support President Obama's military strategy to "degrade and ultimately destroy" the Islamic State in Iraq and Syria.

The strategy deserves support because the other option is to turn away from a situation that the policies of the current and past presidents helped create. Turning away would leave unchecked the particularly virulent form of jihadist bloodletting ISIS represents, allowing it to spread, generating greater chaos and a cycle of sectarian reprisals in the already unstable region.

None of that would be good for the United States. Neither would allowing this non-state entity to control a large territory from which it could prepare for attacks on the United States and its allies, a threat made all the more real by the fact that a small group of witless Americans and Europeans have joined ISIS.

Finally, there is the moral justification to stop a group that is killing or enslaving all who disagree with its particular brand of Sunni extremism, and which has beheaded two American journalists in very public fashion.

In his speech Wednesday, the president said the United States will expand its air campaign to degrade and destroy ISIS military operations and help ground forces - not including U.S. troops - to recapture Iraqi territory from the jihadists. The president also made it official that attacks will extend into Syria to deny any safe haven for ISIS forces.

The president is dispatching another 475 military advisors to assist in training the Iraqi Army, which was embarrassingly routed earlier in the conflict by the much smaller and less-equipped ISIS forces. Left unsaid, apparently for diplomatic reasons, is expected assistance as well to Kurdish forces in the north. It remains to be seen whether Iraqi and Kurdish soldiers can displace ISIS with the help of U.S. air support.

President Obama announced "that America will lead a broad coalition to roll back this terrorist threat." What that coalition will look like is uncertain. The chief executive said it is especially important that it include "Arab nations who can help mobilize Sunni communities in Iraq and Syria to drive these terrorists from their lands."

That's the rub. Overlying this conflict, and complicating the strategy to address it, is the antagonism between Islam's Shiite and Sunni sects in the region, which adds to the difficulty of discerning friends and foes. Yet the leaders of Saudi Arabia, a Sunni nation, genuinely fear the potential for ISIS to generate unrest and rebellion among fellow Sunnis in that country. They have great incentive to see the movement crushed in Iraq.

Helping the territorial success of ISIS in Iraq was the distrust Sunni village leaders had for the Shiite-dominated government. Under U.S. pressure, the new government that recently took power in Baghdad promises to be inclusive, but long-held animosities do not quickly evaporate.

Most challenging, and with the greatest chance for failure, is the plan to extend the fight against ISIS to Syria. In 2011, President Obama encouraged Syrians to overthrow the dictatorship of Syrian President Bashar al-Assad. The president's subsequent refusal to fund sectarian and moderate elements among rebel forces in Syria was a major tactical blunder. Instead, ISIS and other radical jihadist rebel groups emerged as the dominant force opposed to President Assad.

Now the president talks of identifying and arming those forces his administration should have helped three years ago, but which are now weaker. In the lawless territories no longer under control of the Assad regime, chances are high that some of the arms supplied to "friendly" rebels could fall into the hands of ISIS. And in attacking ISIS in Syria, the United States will be doing President Assad's bidding.

Such is the morass that confronts the president's military initiative. It will be long, messy and unpredictable, sure to generate more anger and terrorist recruits among some Arabs, even while helping others.

The most troubling question is whether failure leads to military escalation. That potential perhaps gives President Obama his greatest incentive to make sure this works.