[gr8fl4porsche]

Is the paint coming off down to bare metal, primer, or the original paint?

Metal is easy to identify. Primer would be an off color like tan, gray, red, or flat black. Original paint would be the color of the door jambs.

If its just the repaint coming off, then you can use stripper to remove just the layer that you want - sort of. Work in small areas, apply stripper, and wipe it off. The longer it sits the more layers it will eat through. You will have to experiment.

Sanding will do the same but will take a long time.

I can't see why it would be necessary to go down to bare metal unless you are doing a full restoration and have to check the integrity of the metal, look for bondo, or do rust repairs.