They can and they should. It's very simple. "I didn't see any gun".
Just because someone has told you otherwise doesn't make it so.
You have a duty to refuse to enforce unconstitutional laws. You may take legal arguments from your department or the courts under advisement, but ultimately it is your call and yours alone who you will arrest.
If you can't do that within the bounds of the system then you do it outside of them.
If you can't do it outside of them, the you resign.
Anything else make you a fair target.
Who decides what is Constitutional?
Answer only this question, please.