Clifford Wagner, an 80-year-old Republican in Tucson, Ariz., never cared for President Trump. He supported Jeb Bush in the 2016 presidential primary race and cast a protest vote in the general election for Gary Johnson, the Libertarian nominee. An Air Force veteran, Mr. Wagner described the Trump presidency as a mortifying experience: His friends in Europe and Japan tell him the United States has become “the laughingstock of the world.” This year, Mr. Wagner said he would register his opposition to Mr. Trump more emphatically than he did in 2016. He plans to vote for Joseph R. Biden Jr., the...