Salon.com | A "volunteer" police state
A group of non-Bush supporters are prevented from joining a Bush social security event by "secret service agents" -- apparently because of a "no blood for oil" bumper sticker. The event turns out to have been publicly funded. The agents may, or may not, have been officially 'secret service'.
This was standard operating procedure during Bush campaign events. There must never be any critics near Bush.
It's not surprising, but for the sake of historians it's good to document these things.