MILWAUKEE — In the hours after a would-be assassin fired a bullet through former President Donald Trump’s ear, Panfilo DiCenzo, a 40-year-old Democratic voter from Pittsburgh, drew a simple conclusion about the political effect of the attack: “It definitely is good for Trump.” At a time when President Joe Biden has been struggling to shore up support with fellow Democrats following a miserable June debate performance and shaky cleanup effort, some professional Democratic political operatives said Saturday’s shooting will end up sealing the incumbent’s electoral fate. “We’re so beyond f---ed,” one longtime Democratic insider said, noting that the image of...