This is a rather disturbing Washington Post story about a White House policy of trying to influence journalists and what we saw of protests at events involving George Bush.
... "The rally squad's task is to use their signs and banners as shields between the demonstrators and the main press platform. If the demonstrators are yelling, rally squads can begin and lead supportive chants to drown out the protestors (USA!, USA!, USA!). As a last resort, security should remove the demonstrators from the event site."
Advance teams are advised not to worry if protesters are not visible to the president or cameras: "If it is determined that the media will not see or hear them and that they pose no potential disruption to the event, they can be ignored. On the other hand, if the group is carrying signs, trying to shout down the President, or has the potential to cause some greater disruption to the event, action needs to be taken immediately to minimize the demonstrator's effect."