The drive pulley has come out and thrown the belt. on 2004 Buick Century

The pulley is out of align with every other pulley. It looks like it is coming off the shaft but is not loose. What should I look for?

Asked by for the 2004 Buick Century
The harmonic balancer needs to be replaced! NAPA part # 6005312, that is also the belt drive pulley. Be sure the crank sensor that is mounted behind this part is checked also! If it's damaged have it replaced!
The outer ring that the belt runs on is "pressed" onto the center hub of this balancer and is now letting go but the bolt is still tight holding the center hub in place. It has slipped in other words and MUST be replaced as an assembly!! Don't forget about the crank sensor.!