A record fireworks display proceeds on the National Mall after a 90-minute delay despite extreme heat, lightning and an evacuation order, with organizers launching about 850K shells from 10 sites and military flyovers accompanying the show.The White House's Freedom 250 initiative bills the event as the largest in the capital's history; parades in Washington and Philadelphia are canceled because of the heat and the National Park Service warns that smoke and pollution may cause hours of irritation and health problems.Donald Trump addresses the crowd with patriotic and political language as officials and health experts urge caution for people with respiratory conditions while museums and exhibitions such as "Many Voices, One Nation: In Our Words" open elsewhere.