Ted Koppel, senior news analyst, NPR
Lt. Col. John Nagl, retired, U.S. Army, and president of the Center for a New American Security
The 4th Stryker Brigade, 2nd Infantry Division has left Iraq, marking what President Obama has called the end of America's combat mission in Iraq. But some 50,000 U.S. troops remain in the country. It's unclear if and how their role will change as the mission shifts from combat to support.