Vatican City (CNN) Days before the critical New York primary, one Democratic presidential candidate is somewhere he can't rack up any last-minute primary votes.

Vermont Sen. Bernie Sanders is at the Vatican to address a conference on social, economic and environmental issues.

Sanders landed in Rome on Friday morning, traveling in an escorted motorcade to the Vatican. His wife Jane, their four children and a few grandchildren are traveling with him.

He entered through the Perugino Gate of Vatican City, where he was greeted by a dozen or so expat supporters bearing signs reading, "Rome is berning."

Sanders began his 15-minute speech to the Pontifical Academy of Social Sciences with a showing of solidarity and admiration for Pope Francis, emphasizing their agreement on economic justice.

"There are few places in modern thought that rival the depth and insight of the Church's moral teachings on the market economy," Sanders said, a topic which he himself has been speaking about during the presidential race for months.

His speech Friday largely echoed his regular remarks on the campaign trail in the United States: that the concentration of wealth is in too few hands and the middle class is disappearing.

"We can say that with unregulated globalization, a world market economy built on speculative finance burst through the legal, political and moral constraints that had once served to protect the common good," he said.

After his address, the Vermont senator walked through the same gate and greeted onlookers before briefly speaking to the press.

Sanders had said before the trip that he would be honored to meet Pope Francis. But on Friday morning, Francis sent a note to conference attendees saying that would not be able to attend because he is leaving for a trip to Lesbos early Saturday morning. The Greek island has become a focal point of the Syrian refugee crisis.

The liberal Jewish senator and the leader of the Catholic Church make for odd bedfellows in many ways.

Sanders rails against "the establishment" in all of his speeches, and his progressive platform includes strong support for abortion rights and LGBT rights in contrast to Pope Francis.

Still, Sanders has shown a respect and fondness for the unconventional Christian leader, saying recently in a rally that he is "a very great fan" of the Pope and his messages, namely the need to pay attention to the dispossessed and the idolatry of money.

The campaign's calculation

The Sanders campaign rejects the notion that there is any political motivation behind the trip, instead saying the conference is an opportunity for the senator to spread his message of economic inequality.

"There are some things that are above politics and this is one of those. This is an opportunity for him to speak at the Vatican on the signature works of his life," campaign manager Jeff Weaver said.

Sanders, though, didn't refrain from trumpeting the news on the campaign trail.

At a rally on Saturday in New York City's Washington Heights, he weaved the news of his trip to the Vatican into his stump speech, though he admitted that he does not always see eye-to-eye with the Catholic Church.

"It goes without saying that I have my strong disagreements with certain aspects what the church stands for but (Pope Francis) has been out there talking about the need for a moral economy," Sanders said to a crowd of a little more than a thousand, who cheered when Sanders announced his trip.

Weaver called the Vermont senator "not a scripted person" and expects that Sanders will write all of his own comments with a little input from advisers.

When asked if it was a smart move to take 36 hours to travel out of the country ahead of one of the most important primary elections in the campaign cycle, Weaver took aim at Sanders' opponent, former Secretary of State Hillary Clinton.

"Hillary Clinton has been out of the state on a number of occasions for high-dollar fundraisers," he said. "We think this is a more important reason to leave the campaign trail for the day."

Bill Press, a Sanders support and CNN political commentator, put it more colorfully: "He may be leaving the state to see the Pope Francis. She is leaving the state to see the Pope George Clooney in California ... So both of them are leaving the state.

He also pointed out that Sanders will get "a lot of media attention" on the trip. "I think it's good for him. I think it's a great platform."

But New York Times columnist Charles Blow, also a CNN political commentator, disagreed that the trip made political sense.

"It's a real misstep. If Sanders was leaving the United States to travel abroad to broaden his portfolio of things he could discuss, I think it would be really smart," he said, mentioning topics such as ISIS and U.S. military intervention. "That's not what he's doing. He's basically going to be saying the same thing there that he's been saying here."

Strange bedfellows

Sanders has heavily praised Pope Francis in the past, telling CNN in September he considered him "one of the great moral and religious leaders of our time and in modern history."

Weaver emphasized this week, however, that the visit is about having a more just economic system rather than anti-abortion-rights views or other Catholic positions that are contrary to Sanders.

"Clearly there are issues where they don't agree. But this trip is a trip about the moral economy," he said.

Michael Wear, veteran Democratic strategist and faith outreach director for Obama's 2012 reelection campaign, said he found it interesting that Democrats were looking to Pope Francis for moral authority despite their divergence on many issues. But he said it's not necessarily a bad thing for Sanders to engage with someone with a differing point of view.

"I think Bernie likes to show that his message can reach in a lot of places," he said. "Bernie's been able to show that he's able to get a hearing at a lot of places Hillary hasn't been willing to go or not invited to go."

Arin Acharya, 38, a political science professor, said at a Sanders rally in Syracuse on Monday that he doesn't think it will matter to Bernie supporters that the politician disagrees with the Pope on many issues.

"I believe that the Pope right now is not conservative and is a well-read, very learned person and talks about left politics, workers' disenfranchisement. So I think for hard-core Bernie supporters, it really doesn't matter," Acharya said.

Sister Simone Campbell of Network, a national Catholic social justice lobby, sees some agreement between the Pope and Sanders.

"I do know that the issues that he's been raising about income and wealth disparity are really issues that Pope Francis has highlighted," she said. "There is a bit of synchronicity on that."

But she did point out that there was some dissonance about the trip.

"The thing that's ironic for me about the Democratic candidates is that neither of them has really spent much time addressing faith," she said.

One Sanders supporter thought that it was a "valid concern" that the Catholic Church and Sanders' message conflict in some ways, but he added that he doesn't think the trip diminishes the politician's credibility.

"Sometimes you need to find your allies. You may have your disagreements along the way, but if you can share a similar common goal you can convince them to see the light," said Peter Dumbadez, 29, an architect who lives in Brooklyn and came out to see Sanders at rally Wednesday in Washington Square Park in Manhattan.

Will Sanders win Catholic votes?

While the Sanders campaign maintained that the trip is not a political one, others see such a motive at play.

"My first impression when I heard the news was (that) the timing in terms of the states that are coming up could not be more perfect," Wear said.

"It's late in the game, but Pennsylvania and Maryland are huge white, working-class Catholic states," he said, referring to Sanders' delegate gap with Clinton. "The trip is well worth the time. At this stage of the process, Sanders is not going to win this thing without some sort of major shakeup."

Campbell, too, saw politics in the move.

"My political self, when I heard that, I thought, 'Oh, isn't that convenient,'" she recounted. "I think there is some political piece to it."

Christopher Hale, the executive director of the Catholics in Alliance for the Common Good, views it as a politically advantageous move for Sanders -- even if a bit of a gaffe on the part of the Vatican.

"He's speaking four days before the New York primary, so he's definitely taking a gamble by going to Rome. I don't think the Vatican officials who invited him knew they were getting immersed in a political fight like they are," he told CNN, stressing that the Vatican is by no means endorsing a candidate by hosting Sanders.

But he added that it's still a boon for the Democratic candidate.

"There's no way this isn't a win for Bernie Sanders," Hale said, "getting a chance to talk about issues that are very important to him and talk to a very prominent audience."

Lorenza Giammelli, 74, an Italian-American from Syracuse, is a practicing Catholic and a Bernie supporter. In her eyes, the trip is "wonderful."

"I think it's a very smart move," she said. "I think it's good for the Pope, it's good for (Bernie), too.