Why are the USA Troops carrying their rear ends day in and day out?

Source: CNN News. USA Newspaper. ABC News. NBC News. NOTE: Four years and the killings in Iraq go on and on. Into the 5th year now. All I see on T.V is the Army and Marines with a thousand yard stare carring their rear end in their arms. The insurgents are hurting the powerful Marines and Army everyday and making the Marines/Army beg for safety every hour they stay in Iraq. Time for the troops to come home. The war can't be won.