He described a troop increase as "the least bad option" and said it could cost him his shot at the presidency.
Three other senators proposed a resolution against a troop increase in Iraq.
Ms. Brown said she agreed with the troop increase "if it would settle things down over there so the guys can come home."
The bigger question is whether Congress will seek to stop the troop increase.
The last remaining American units in the troop increase are just now arriving.
The comments came on a day the administration stepped up its campaign against Congressional opposition to the troop increase.
The troop increase sent a shudder through both the alliance and among many Americans.
"The recent troop increases were not the product of consultation," he said.
The message is aimed in part, officials say, at trying to build domestic support for a troop increase.
Congress is poised to pass a resolution denouncing the troop increase.