But that was largely forgotten - or at least ignored - when Mr Trump swept up to St Peter's Square in a 50-car motorcade, to be met by Swiss Guards in traditional harlequin uniform.
Officials in Jerusalem and the Vatican have been discussing the possibility of Pope Francis visiting Israel this coming autumn, Channel 10 reported on Thursday.
The pope's interpreter could be heard translating a comment by the pope to the Slovenian-born First Lady: "What do you give him to eat?" In that vein, a key exchange of the meeting was his gift to the president: copies of his three major writings. 'I won't forget what you said, ' he told the pope after their meeting.
"He is something", Trump said of the Pope. "I am proud to be a Christian and as President I will not allow Christianity to be consistently attacked and weakened", Trump said.
The two men's worldviews collided head-on early past year, when Francis was sharply critical of Trump's election campaign pledge to build an impenetrable wall on the Mexican border and his declaration that the United States should turn away Muslim immigrants and refugees.
No further details, such as when the first lady became Catholic, were given.
It remains unclear whether the Twitter banners will keep changing as the president's inaugural four-nation trip continues, but Trump was certainly impressed by his visit to the Vatican.
Mr Trump gave the pope a boxed set of five first-edition books by murdered United States civil rights leader Martin Luther King.
While walking down the red carpet after their arrival, Trump reaches out for Melania's hand, only to be rejected.
There's been a lot of attention on Donald Trump's hands during his first foreign trip as U.S. president.
VATICAN CITY-It could have caused a diplomatic incident but a culinary quip from Pope Francis seemed to have gone down well with Donald Trump and his wife Melania.