I had a 2004 Chevy Impala, same body type.
The only way this would happen is if one of them was bent. If it's catching, bend it back.
Carrying Place, ON
reply to jsouth
Do you know what changed to cause this? Are the the door hinges sprung, or was there some sort of impact that changed the alignment of the door or fender?
If you're looking for a quicky, do it yourself fix try this, my take on how to "bend it back" gently.
Have a good look at the passenger door to fender gap to see what it should look like. Use this as your guide.
With the driver door closed, use a paint stir stick (or anything gap sized that won't break off the paint easily) to pry the fender out to the same level as the door. It may need to come out a bit further if you are compensating for damage.
If the paint stick won't fit, you may have to open the door a bit, put the paint stick in place and gently close the door while prying the fender out. Loosening the fender mounting screws/bolts at the bottom of the door to fender seam would help this go easier.
Essentially, you need to correct the shape of the fender at the door seam.