President Donald Trump on Monday offered brief condolences over the passing of Pope Francis, but the two men clashed repeatedly, including as far back as Trump's 2016 presidential campaign, over how to treat migrants.

By the time Francis took over as leader of the Catholic Church in 2013, meetings between the president and the pontiff had become commonplace. During the dozen years that he served as the pontiff, Francis, who died April 21, met each of the three men who served as the U.S. president during his papacy.