Biden’s campaign has been jackhammering home the premise that he is best suited to winning a general election against an incumbent who must not be re-elected. Biden says he is running to achieve three main things, none of them distinguishable from what he might have said when he ran in 1988 and 2008: 1) to lead the “battle for the soul of America,” 2) to restore the middle class and 3) to unite the country. He also says that he was inspired to run for president in 2017 after seeing how Mr. Trump responded to violent clashes involving white nationalists in Charlottesville, Va.