Best way to remove primer from a urethane front bumper?

[BlueOvalStangGT]

I messed up on my front bumper and had some bubbles. After some sanding this is what it turned into:

Before:

After:

Im really not to comfortable painting the bumper if this possibly happened in other places, so I was going to strip it down and try again. Can I use some kind of chemical to strip the paint (note it is a urethane bumper) or do I have to start sanding with some like 180 grit? What would you guys do?

 

[Turbo92PGT]

I would use 180 grit paper on a DA (by hand would take forever). and just feather the primer back untill it stops cracking and you get the imperfections (bubbles) or whatever out that you want.

What kind of primer/ base/clear are you using?