President Barack Obama's decision to arm the rebels in Syria became inevitable once Bashar Assad used chemical weapons against his own people, but that doesn't make it any less regrettable. When he said in December that was a red line for the United States and there would be consequences for Assad if he crossed it, Obama unfortunately, boxed himself in.

Assad has to go. Obama has made it clear that's the outcome he wants. But arming the rebels, whose ranks include militant Islamists, is a risky gambit. Who gets the firepower? If Assad is toppled, factions hostile to the United States could take control.

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But the two-year uprising to remove Assad's brutal regime is going badly. According to a U.S. intelligence assessment the White House revealed Thursday, he has used chemical weapons, including the nerve agent sarin, multiple times in the last year in attacks that killed 100 to 150 people. And with weapons from Iran and the help of fighters from Hezbollah, a terrorist organization based in neighboring Lebanon, Assad now has the upper hand in the civil war that has already claimed 93,000 lives.

Obama has been unsuccessful in persuading Assad to negotiate with rebels. But there is a chance -- however remote -- that the prospect of a better armed opposition could nudge Assad to the table. And the pressure will be on Obama to rally international opposition to the Syrian president, both at the United Nations and at next week's meeting in Northern Ireland with the Group of Eight, the world's richest nations.

But after arming rebel fighters, Obama must not allow the United States to be drawn further into the bloody Syrian civil war.

A decade of fighting in Iraq and Afghanistan has left the American public justifiably war weary. And with a ruthless Syrian regime pitted against militant Islamists, it's a no-win situation for the United States.