Pope Francis is greeted by Secretary of State John Kerry and other members of Congress at the Capitol on Thursday. (Photo: Mark Wilson/Getty Images)

Attendees of Pope Francis’ speech to Congress on Thursday morning had been drilled on the proper protocol to observe. This was not a State of the Union address, which normally begins and ends with glad-handing. There was to be no hugging of the pope. No sticking out hands to shake. Absolutely no selfies.

And so as the pope entered the House chamber, he was able to make his way down the aisle quickly, with small nods here and smiles at the members of Congress who stood applauding and trying as hard as Catholic schoolchildren to be good. As Francis reached the front of the room, however, he turned and approached a startled Secretary of State John Kerry with his hand extended. The two exchanged brief words, and the pontiff continued to his place behind the podium.

That single handshake speaks volumes about how Pope Francis has impacted American Catholicism.

When Kerry ran for president in 2004, he was the first Catholic nominee since John F. Kennedy more than 40 years earlier. Far from needing to prove that he would not take orders from the Vatican, Kerry was dogged by criticism from conservative Catholic leaders over his support for abortion rights. Then-Archbishop Raymond Burke declared that Kerry should be denied the Eucharist, and the candidate’s campaign ended up adding a communion check to its advance work, calling ahead on the trail to confirm that the church where Kerry would attend Mass on a given week would allow him to receive communion.