As the Syrian government cracks down brutally on the opposition, calls to protect civilians are growing louder. But many defense experts warn against military intervention.

The messages coming out of Washington these days are loud and clear. "(Bashar al-Assad) must step aside and allow a democratic transition to proceed immediately," Obama said over the weekend. "Your days are numbered," said Susan Rice, US Ambassador to the United Nations, delivering a message to the Syrian president in an interview with CNN.