A rebel fighter takes aim during a training session in Eastern al-Ghouta, a rebel-held region outside the capital Damascus, earlier this month. Russia is inviting Syrian opposition groups to peace talks in Moscow, but few of them want to go to a country that supports Syrian President Bashar al-Assad. Abd Doumany/AFP/Getty Images hide caption

itoggle caption Abd Doumany/AFP/Getty Images

President Obama walks out of a meeting with the Senate Democratic Caucus at the Capitol on Tuesday. Michael Reynolds/EPA /LANDOV hide caption

itoggle caption Michael Reynolds/EPA /LANDOV

A rebel fighter raises his weapon after firing a missile Sunday toward Syrian government troops in the northern city of Aleppo. Syria's largest city has been the scene of heavy fighting for the past three months. Both sides control part of the city, and the fight has been a stalemate recently. Narciso Contreras/AP hide caption

itoggle caption Narciso Contreras/AP

An image taken from video obtained from the Shaam News Network, authenticated by AP reporting, shows attempts to rescue the wounded in Idlib, northern Syria following heavy bombing from military warplanes. Uncredited/ASSOCIATED PRESS hide caption

itoggle caption Uncredited/ASSOCIATED PRESS