Pope Francis traveled to Ciudad Juarez, the Mexican city which borders El Paso, Texas, to celebrate Mass on the final day of his five-day visit to Mexico with his outspoken comments getting praise from some quarters.

But Donald Trump derided the Pope for saying the U.S. Republican Party presidential candidate hopeful cannot claim to be a Christian and also pledge to build a wall along the Mexican border to shut out immigrants.

"Anyone, whoever he is, who only wants to build walls and not bridges is not a Christian," Francis set on the papal flight from Mexico.

"Vote, don't vote, I won't meddle. But I simply say, if he says these things, this man is not a Christian," Francis said.

"We need to see if he really said them and for this I will give him the benefit of the doubt."

On a campaign stop in South Carolina, which holds its Republican primary this weekend Trump hit back saying, "For a religious leader to question a person's faith is disgraceful.

"I am proud to be a Christian and as president I will not allow Christianity to be consistently attacked and weakened," said Trump who is a Presbyterian.

"For Pope Francis, who ended his visit to Mexico on Feb. 17, there were few topics or institutions too taboo to tackle," wrote Ana Campoy in Quartz.

But at least one commentator found Francis not hitting the key notes in speaking with compassion for justice in the world's second biggest Catholic nation.

"During his six-day stay, he took on drug trafficking, the government's failure to provide economic opportunity, corruption, discrimination, human trafficking, and even employee exploitation," Campoy, however extolled.

"He's really taking off the gloves," Andrew Chesnut, Chair in Catholic Studies at Virginia Commonwealth University, tells Quartz. "We haven't seen him this prophetic and this outspoken in any of his previous national tours."

At the Mexico-U.S. border town of Ciudad Juárez, just a few years ago one of the deadliest places on earth, he compared Mexico to Nineveh, an ancient city "so used to degradation" that its inhabitants had lost all sensibility to pain.

"No more death, nor exploitation!" he said during a mass in the border city. "There's always time to change."

Francis told hundreds of thousands of people present to beg God for the "gift of tears" over the suffering of others, especially forced migration.

"Let us together ask our God for the gift of conversion, the gift of tears, let us ask him to give us open hearts," he said during the mass at Benito Juárez stadium.

"No more death! No more exploitation!"

Francis was the first pope to be received at Mexico's National Palace, the seat of the executive power.

Still he criticized his hosts. After shaking President Enrique Peña Nieto's hand, he essentially laid down the blame for the country's biggest problems at the feet of its ruling class.

CHIDING MEXICANS

The Pope also scolded all Mexicans, including the Church, for failing the country's indigenous communities, which are Mexico's poorest.

When he spoke in the southern state of Chiapas, where about a quarter of the population is indigenous, he said the world has much to learn about their culture.

Instead, however, it has "systematically and structurally" excluded them and snatched their lands.

"How sad!" he said. "What good it would all do us to examine our conscience and say 'Sorry!'"

The presence of the first Latin American pope at the border also symbolically puts the most influential religious leader on the global stage squarely in the middle of a fierce presidential election-year fight over immigration, wrote John Gehring in The Washington Post.

Donald Trump has called the Pope, a week earlier, "a very political person" and implied Francis was being used by the Mexican government.

"I think Mexico got him to do it because Mexico wants to keep the border just the way it is because they're making a fortune and we're losing," Trump moaned.

Gehring wrote, "A pope who travels to the margins as a witness to God's solidarity with the poor and vulnerable isn't playing politics.

"He is following the Gospel. In the parable of the Good Samaritan, Jesus radically redefined the definition of neighbor beyond language, religion and border."

Trump is onto something, wrote Gehring. "In the best sense of the word, Pope Francis is political.

"A good Catholic meddles in politics," the Pope has said, a pithy summation that reflects centuries of Catholic teaching that views the common good and human dignity as the ultimate aim of politics.

But commentator Miguel Guevara, wrote in Al Jazeera America that the Pope's visit to Mexico was disappointing.

"Many assumed that he would be especially bold in a country that has known no end to the violence that started with the so-called war on drugs," wrote Guevara.

"Francis found a country that has steadily become less Catholic.

"While 50 years ago, virtually every Mexican considered himself or herself a Catholic, nowadays, only 4 in 5 Mexicans do so.

"Catholics in Mexico are mainly clustered in the center of the country, with the indigenous south shifting toward other forms of Christianity. Islam has been on the rise in Chiapas, a largely indigenous state that Francis visited."

'ANODYNE MASSES'

Guevara said, "His Masses in Mexico have been largely anodyne. He focused on one of his main talking points, inequality, while skipping any thorny local political issues."

When the Pope flew to Ecatepec, a gray slum on the outskirts of Mexico City with a representative sample of the half of Mexico's population living in poverty.

There he addressed the country's glaring disparities and mourned the deaths of those who make the journey to the U.S. at the hands of "dealers of death."

"However, his speech and visit largely avoided addressing any controversial topics. In the months before his trip, the parents of the 43 college students from Ayotzinapa who disappeared a year and a half ago asked him to meet with them.

He did not see them, but they were invited to a mass he held in Juárez, Vatican spokesman Federico Lombardi said.

"The Mexican government might have had an influence on Francis' message," speculated Guevara.

"While he scheduled symbolic stops on his visit, he largely failed to address the epidemic of violence in Mexico," noted the writer who said that in a visit to the western state of Michoacán, Francis barely mentioned the role of drug dealing in the carnage.

"This is especially disappointing, since Michoacán has been one of the states hardest hit by drug violence. In fact, it was in Michoacán that President Felipe Calderón launched the country's war on drugs in 2006."

Guevara said that, "While Francis has been known as a poignant political messenger, he largely failed in Mexico."