On the flight, the pope nevertheless appealed again to Mr. Trump, this time on his decision to end President Obama’s Deferred Action for Children Program, known as DACA. The program allows children brought illegally to the United States to stay without fear of deportation. Mr. Trump has given Congress, which has failed to pass immigration overhaul for the last decade, six months to enact legislation to resolve the status of about 800,000 people affected by his decision.

The pope, echoing the excoriation of the United States Conference of Catholic Bishops – which called the president’s decision “reprehensible” — argued that the removal of children from families hurt both children and parents.

“I hope they rethink it a bit,” he said. “Because I heard the U.S. president speak. He presents himself as a man who is pro-life. If he is a good pro-life believer he must understand that family is the cradle of life and one must defend its unity,” said Francis, who in the past has said that advocates, like Mr. Trump, of a wall to keep out migrants on the Mexican border were “not Christian.”

The pope spoke on the papal plane after a five-day trip to Colombia during which he sought to sustain a fledgling peace process between the government and the rebels of the Revolutionary Armed Forces of Colombia, beatified two priests slain in the war, made an important change to the church’s liturgical rules and sustained a black eye when his popemobile stopped short in a crowd of pilgrims.

(“I was leaning over to greet children,” he said “and I saw the glass, and boom!”)

In contrast to his negative appraisal of Mr. Trump’s approach to immigration, the pope praised Italy’s efforts to welcome large numbers of migrants even as it sought to stem the tide of immigrants coming from Libya. Italy, he said, appeared to be “doing all it can with humanitarian care” and had a right to consider the realities of integration and manage the influx.