Callista Gingrich, U.S. ambassador to the Holy See, presents her credentials to Pope Francis during a private audience at the Vatican on December 22, 2017. (© L'Osservatore Romano/AP Images)

Callista Gingrich, U.S. ambassador to the Holy See, presents her credentials to Pope Francis during a private audience at the Vatican on December 22, 2017. (© L'Osservatore Romano/AP Images)