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Demonstrators make a futile attempt to stop a Chicago police officer from detaining a protester during this weekend's NATO summit in Chicago Sunday, May 20, 2012 in Chicago. (AP Photo/Seth Perlman)

Protesters swarm on final day of NATO summit

Demonstrators launched another round of protests May 21 in the final hours of the NATO summit, marching through an unusually quiet downtown Chicago to the headquarters of Boeing and President Barack Obama's campaign.