During a visit to Mexico, Pope Francis said in 2016 of Trump,

A person who thinks only about building walls, where they may be, not not building bridges, is not a Christian. This is not in the gospel. As far as what you said about whether to vote or not vote, I am not going to get involved in that. I only say that this man is not a Christian if he has said things like that.

In a retort, Trump said that the Pope was being manipulated by the Mexican government. He replied at a rally,

If and when the Vatican is attacked by ISIS, which as everyone knows is ISIS’s ultimate trophy, I can promise you that the Pope would have only wished and prayed that Donald Trump would have been President because this would not have happened.

Trump has repeatedly referred to himself as a Christian, though he was unable to recite a single verse from the Bible. He also had fairly positive views of Pope Francis upon the pope’s election.

In another tweet, Trump linked the humbleness of the Pope to his own. Trump also bragged about his own humility during the 2016 campaign.

Pope Francis’ views of Trump continued to be more mixed.

During a 2017 visit to the Vatican that was described as “stiff,” Pope Francis gifted Trump with copies of his writings, including an encyclical on climate change. Trump has derided climate change as a Chinese hoax.

Pope Francis also criticized Trump’s border and family separation policy, comparing it to the Berlin Wall.

It falls into the greatest cruelty. To defend what? The territory, or the economy of the country, or who knows what? We already know one wall, the Berlin Wall that brought us enough headaches and enough suffering…. But it seems that man does what animals do not do, doesn’t it? Man is the only animal that falls twice into the same hole.

On Trump’s move to repeal DACA, the Obama-era Deferred Action for Childhood Arrivals, Pope Francis said,

The president of the United States presents himself as pro-life and if he is a good pro-lifer, he understands that family is the cradle of life and its unity must be protected.

The Hill – Pope Francis appears to knock Trump with appeal to build bridges instead of walls
NPR – ‘He Is Something’: Trump Visits Pope Francis At The Vatican
America Magazine – Pope Francis calls Trump’s border policy ‘cruel,’ compares southern barriers to Berlin Wall
CNN – Pope Francis says rescinding DACA is not ‘pro-life’