"Use the attack to garnish a little media time. Clearly, someone is illegally interfering with your first amendment rights, and the electoral process. Don't forget to take plenty of photos, and circulate them around."
Yes. Sadly, it's not just Republican signs and stuff that are being vanadalized. Plenty of action the other way, too.
Personally, I'd like to see some serious enforcement action on the part of law enforcement against any political vandalism, no matter on which side.
As you say, these are our first amendment rights. Nothing is more precious.