After long and costly U.S. wars in Iraq and Afghanistan, President Obama has been deeply reluctant to act forcefully in Syria. But reports last week of a possible chemical weapons attack in Syria appear to have changed the White House's tone. As NPR's Larry Abramson said on Morning Edition, the issue now appears to be "how to respond, not whether to respond."

"The president's response this time has to be significant," Aaron David Miller, a distinguished scholar with the Woodrow Wilson International Center for Scholars, said on the same program. "It cannot simply be a couple cruise missiles into a storage shed somewhere. It's got to look real. It's got to look credible, if in fact it's going to serve to deter future use of chemical weapons."

So what, exactly, will the U.S. do in Syria? Here are some options:

Limited Military Action

The U.S. and its allies could target Syrian command-and-control sites with cruise missiles fired from Navy ships. Fighter jets are also ready, but ABC News reported that they won't cross into Syrian airspace.

American boots on the ground have always been considered highly unlikely, and that scenario hasn't changed. Russia, which supports and arms the Assad regime, is considered highly likely to veto any U.N. backing for an international military intervention. However, the U.S. is talking to its allies in Europe and elsewhere about possible coordinated action.

Establish A No-Fly Zone

Sen. John McCain and others have called for the U.S. to set up a no-fly zone that would create safe havens inside Syria. But Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, noted in July that such an effort could cost $1 billion a month.

Arm Syrian Rebels

Syrian government troops have made advances in recent months against the rebels, who want help in the form of weapons. The rebels already receive some weapons from Gulf allies. The White House did agree to provide military assistance earlier this summer, but the details are not yet clear. The U.S. is also concerned that weapons for the rebels could end up in the hands of extremist groups that have been playing a prominent role in the fighting.

Nonmilitary Options

The Washington Post's Max Fisher listed nonmilitary options the U.S. has in Syria. These include more humanitarian aid within Syria and inside refugee camps in neighboring countries; intelligence-sharing with rebels; sanctioning covert action inside Syria by regional allies; reaching out to Russia, an Assad ally, for support on action by the U.N. Security Council.

Do Nothing

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