Pope Francis is questioning whether someone with President Trump’s views on immigration should really be considered “pro-life,” reigniting a feud between the major world leaders that famously boiled over during the presidential race.

“I have heard the president of the United States speak,” Francis said aboard the papal plane on Monday, reported the National Catholic Reporter. “He presents himself as a pro-life man. If he is a good pro-lifer, he should understand that the family is the cradle of life and you must defend its unity.”

The pontiff was responding to a question from a Mexican reporter about Mr. Trump’s decision to end the Deferred Action for Childhood Arrivals program, known as DACA, which granted a two-year stay of deportation to illegal immigrants who were brought to the country as children.

Francis levied a similar charge against Mr. Trump during the presidential race, when he said someone “who thinks only about building walls” and not “building bridges is not a Christian.” Mr. Trump, who called those comments “disgraceful” at the time, has yet to respond to the pope’s latest barb.

By questioning Mr. Trump’s pro-life bona fides, Francis echoed a popular progressive talking point — that abortion opponents are not living up to the “pro-life” mantra when they reject progressive views on issues ranging from welfare to immigration and the environment.

Indeed, Sen. Elizabeth Warren, Massachusetts Democrat, made this argument on the Senate floor in June during debate over Obamacare repeal, calling the pro-life label the “biggest political play of all.”

“Calling something ‘pro-life’ won’t keep women from dying in back-alley abortions,” Ms. Warren said at the time. “It won’t help women pay for the cancer screenings that could save their lives. It won’t help them take care of their families, have safe sex or afford their medical bills. The pro-life label is the Republicans playing politics with women’s lives.”

Jay Richards, research professor at The Catholic University of America, said the line of argumentation is a “common progressive ploy to try to claim that Republicans aren’t really ‘pro-life’ because they disagree with progressives on other issues.”

“I simply reject the progressive argument that Republicans who are pro-life and also pro-economic freedom are somehow contradictory,” said Mr. Richards, who is executive editor of “The Stream.” “The reason I support the economic views I do — the value of private property, the value of limited government, the value of economic freedom — is because I think demonstrably where those things are present, more human beings flourish and more people emerge from poverty. And I think the empirical facts bear that out.”

But Patrick Carolan, executive director of the Franciscan Action Network, said Francis was right to question Mr. Trump’s commitment to the pro-life cause. He said opposing abortion does not automatically make someone “pro-life.”

“You can believe what you want to believe, but you’re not pro-life if you’re in favor of nuclear weapons,” Mr. Carolan said. “You’re not pro-life if you’re in favor of the death penalty. You’re not pro-life if you’re not welcoming of the stranger.”

In the interview aboard the papal plane, Pope Francis also said political leaders have a “moral responsibility” to cut carbon emissions in order to prevent climate change.

“If someone is a bit doubtful … ask the scientists,” the pope said in response to a question about catastrophic weather events. “They are very clear. They are not opinions on the fly. They are very clear. Then decide, and history will judge the decisions.”

Asked why political leaders have not done more to curb carbon emissions, Pope Francis paraphrased a passage from the Old Testament.

“A stubborn [animal] that does not see,” the pope said, reported NCR. “The human is stupid, the Bible says. When it does not want to see it does not see. It sees only a part.”