From the letter:
Mayor, you and your coalition of allies have misrepresented yourselves to the mayors of America and its citizens. This effort is simply another attempt to shift blame for violent crime from criminals to law-abiding gun owners. This is gun control, not crime prevention. These tactics do not target illegal guns, but rather honest citizens and lawful dealers, essentially criminalizing all gun ownership. This coalition makes no distinction whatsoever between law-abiding gun owners and violent criminals.Bitter over at SIH has recently done a multi-post series on efforts along these lines for PA.
One Mayor at a time.