NEW : While the total number of U.S. troops in Iraq will continue to diminish throughout 2011 , the withdrawal rate will be `` calibrated and adjusted based on conditions on the ground , '' according to presidential national security adviser John Brennan . U.S. troop withdrawal rates will depend on ground conditions , Brennan says . The drop comes ahead of President Obama 's Monday deadline . Iraq troops will now switch to an advice-and-assist role . Vice President Obama says American security forces are now successfully protecting U.S. .
NEW : U.S. troop withdrawal rates will depend on ground conditions , Brennan says . The drop comes ahead of President Obama 's Monday deadline . Iraq troops will now switch to an advice-and-assist role . Vice President Obama says American security forces are now successfully protecting U.S. .