President Trump used an elaborate fireworks display and Air Force One flyover at Mt. Rushmore on Friday night to rally his base, ushering in Fourth of July celebrations a day early with accusations that a “new far-left fascism” is part of “a merciless campaign to wipe out our history.”The combative address in South Dakota, using one of the more dramatic and historical backdrops of his presidency, came as Trump trails badly behind Joe Biden in public opinion polls amid a rapidly spreading pandemic, high unemployment and a national reexamination of the role of racism in American history, policing and culture.Trump has indicated repeatedly — sometimes employing racist rhetoric or dog whistles — that he believes his best hope at victory lies in rallying his largely white voting base around the idea that demands for change amount to an attack on American values and culture. In Friday’s speech, he aimed exclusively at those voters, making few concessions to the usual July Fourth traditions of national unity. “Make no mistake,” Trump told several thousand people, packed tightly into the amphitheater near the monument, mostly without masks, chanting “USA” as they cheered him on, “this left-wing cultural revolution is designed to overthrow the…