Pope Francis held strong relations with the United States throughout his papacy, and his visit to Washington in 2015 was historic. (AP Video: Mike Pesoli)

For six days in September, 2015, Pope Francis made a historic visit to the United States, visiting some of the country's biggest cities and speaking to massive crowds of the faithful along the way.

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.

Cardinal Kevin Farrell was handpicked by Pope Francis to be camerlengo, which involves running the Vatican in the days between when a pontiff passes away and another is chosen. NBC News’ Anne Thompson reports Farrell spent much of his priesthood in the United States.