Protesters rally in Chicago on Sunday, May 20, the first day of the NATO summit. A week of demonstrations led up to the two-day meeting, which brought together the leaders of more than 50 nations. Getty Images

A demonstrator displays an anti-NATO button on his bandana Sunday. Largely peaceful crowds chanted, waved signs and banged drums in Chicago. Getty Images

Members of the anti-war group Code Pink demonstrate in Chicago on Sunday. Getty Images

Two men rest against a tree before the start of protests on the first day of the NATO summit. Getty Images

A police officer and a protester face off with cameras in Chicago during a demonstration organized by National Nurses United on Friday, May 18. Friday was the fifth day of protests leading up to the NATO summit. Getty Images

Officers form a line to prevent protesters from crossing the Michigan Avenue Bridge during protests on Friday. Getty Images

Protesters make their way through downtown Chicago in an impromptu demonstration. Getty Images

Police clash with protesters attempting to cross the Michigan Avenue Bridge in Chicago. Getty Images

Chicago police watch over protesters during demonstrations organized by National Nurses United in Daley Plaza in Chicago. AFP/Getty Images

An Occupy Wall Street protester in Chicago covers himself with an American flag after a march through downtown Chicago on Friday. AFP/Getty Images

A souvenir shop window reflects protesters in Chicago on Thursday as they demand an end to NATO violence ahead of the summit. AFP/Getty Images