Barack Obama will meet Pope Francis for the first time Thursday for talks on a shared agenda to fight inequality which the US President hopes will help boost support at home.
The talks between the first Latin American pope and the first African-American US president will focus on tackling the gap between rich and poor, but could spill over into thornier issues such as abortion, contraception and gay rights.
"The Holy Father has been an inspiration to people around the world, including me," Obama said in an interview with the Italian daily Corriere della Sera published on Thursday.
"It doesn't mean we agree on every issue," he added.
The meeting at the Vatican comes as a welcome rest-stop for Obama during a six-day European tour dominated by the crisis over Crimea, and the US leader will doubtless be hoping some of the pope's overwhelming popularity will rub off on him.
Obama is "mostly going I think to bask in the glow of the new Pope," said Jeremy Shapiro, visiting fellow at Washington's Brookings institute.
His main aim will be "to highlight their sort of mutual attention to the problems of poverty and inequality. This isn't really a foreign policy stop," he said.
Ahead of the meeting with Obama, Pope Francis held a morning mass for a group of 500 Italian politicians in which he warned them against becoming "hard-hearted" and "corrupt".
Politicians are "fishermen" and "should not distance themselves from the people, close themselves in their group, their party," the pope said.
Obama will also meet new Italian Prime Minister Matteo Renzi -- the European Union's youngest government leader -- and President Giorgio Napolitano during his visit, as well as going on a private guided tour of the Colosseum.
Diplomatic relations between Italy and the United States are close, though Rome still needs some convincing on the value of imposing sanctions on Russia over the Ukraine crisis, amid fears it would take a toll on a key market.
Obama in his interview highlighted the "critical role" played by Italy in the Mediterranean region and said Washington and Rome were working together to rebuild Libya.
Italy's 39-year-old Renzi, who used Obama-style catchy slogans and social media campaigns to shoot up the political ladder, will be keen to strengthen ties with the US leader.
The White House said Obama hopes to speak to the pope about their "shared commitment to fighting growing inequality", though the peace process in the Middle East, the environment and immigration are also expected to be on the table.
Earlier this month, he used the National Prayer Breakfast in Washington to argue that his calls for tax hikes on the rich and curbs on abuses by big banks had a strong moral and religious grounding, in an election-year swipe at Republicans.
Religious observance should guide political motives and lead to policies that help the sick and the needy, he said -- echoing Francis's rallying cry for action against poverty.
However, Vatican experts say the relationship is not as cosy as it once was between pope Jean Paul II and Ronald Reagan, and Francis is unlikely to refrain from tackling Obama on his domestic and foreign policy.
The pontiff spoke out strongly against a proposed military intervention by the US in Syria last year, organising a vigil at the Vatican which drew tens of thousands of people.
US Catholic leaders have repeatedly challenged Obama's signature accomplishment, the Affordable Care Act, arguing that it violates religious freedom by requiring for-profit corporations to provide insurance for contraception.
Controversy surrounding the Affordable Care Act and Obama's drop in popularity risk resulting in a Republican victory in an upcoming Senate election, which would dramatically weaken the US leader for his remaining two years in power.
Religious expert John Allen told Vatican Radio Obama will be fishing for Catholic votes to help him hold on to the Senate.
Words of support from Francis would certainly boost his case: a survey by Saint-Leo University found Francis was popular with 85 percent of Catholics and 63 percent of Americans.
A survey published last month by CBS News and the New York Times meanwhile put Obama's approval rating at 41 percent.