President Trump and Pope Francis have little in common. One rose to power championing his wealth and machismo, the other on a platform of humility and mercy. One wants to build a wall to keep migrants out, and the other preaches to welcome the stranger. When they meet for the first time on Wednesday morning in the Vatican’s Apostolic Palace, their competing visions of greatness will come to a head—with diplomatic and political consequences. Trump’s break with his predecessor, on nearly every issue, has raised questions about how the U.S.