MOSUL is the good girl who went bad. Quiet in the early days of the occupation, the violence-ravaged Iraqi city has become a must-win battlefield for our enemies. The terrorists and insurgents will throw all they have left into the fight. There's no mystery involved: Mosul's the decisive point in northern Iraq. Over the long term, the city's vastly more valuable than Fallujah. Insurgent attacks, terrorist bombings and assassinations erupted last autumn and continue on a regular basis. They're not going to stop soon. After Baghdad, Mosul will remain the most bitterly contested Iraqi city in the months ahead. Every...