President Obama is taking a prudent step in deciding to send military support to Syrian rebels after a two-month investigation produced near certainty that the regime of President Bashar Assad has used chemical weapons in its fight for survival.

Nevertheless, no one should doubt the significant risks to the Middle East and potentially the United States as this country lends increasing weight to this fight.

The question of arming the Syrian rebels or of otherwise intervening in this fight has been raging within the Obama administration almost since the rebellion began. The president, himself, has resisted, and not without reason. Arms meant for rebels could wind up in the hands of terrorists, possibly in Afghanistan where they might be used against American troops. This country is also weary after nearly 12 years of war and the loss of thousands of lives and billions of dollars.

Yet there has always been an argument for some greater involvement by this country, whether it was through arms or the establishment of a no-fly zone or air strikes to hamper Syria’s ability to fight the rebels who, whatever their backgrounds, are understandably determined not to live under Assad’s brutal regime.

Today, the risks are amplified. Assad has made gains against the rebels because thousands of Hezbollah fighters have flooded into Syria. Alone, that risks a wider war. American involvement can only heighten that risk.

Yet, a human crisis is unfolding in Syria, where an estimated 90,000 people have died in the past two years. If Assad were to prevail, the retribution would be fearsome. It won’t be bloodless if the rebels win, either, and there is no telling at this point into what direction the country might spin. This is a matter of making the least bad choice.

With proof of the use of chemical weapons, including the nerve agent sarin, Syria has crossed Obama’s “red line.” It is time to act, though Obama should be prepared to resist, as necessary, the predictable demands for more.

Indeed, no sooner did the administration announce its plans to escalate its involvement in this war than those calls began: from House Majority Leader Eric Cantor of Virginia, from Sen. Lindsey Graham of South Carolina and from Sen. John McCain of Arizona.

They may be correct, but Obama should not presume them to be so. As Iraq should have taught us, going in is not always wise.

What is the end game? Who will set up a new government? Will the United States be a captive of post-war Syria as it has been of Iraq and Afghanistan?

We need to be more involved, yes, but we also need not to be reckless.