FALLUJAH, Iraq -- Iraqi troops led by one of Saddam Hussein’s former generals began replacing Marines here Friday as a plan to end a monthlong siege of this battle-torn city gained momentum. Former Iraqi Gen. Jassim Mohammed Saleh, dressed in the uniform of Saddam’s Republican guard, entered Fallujah to cheering crowds, triggering a debate in the United States on whether securing the defiant city with an Iraqi force was a masterstroke or a concession that could undermine U.S. control of the country. “I am very happy to be here, you are truly a friend,” Saleh, hand-picked to head the new...