In a rare gesture, President Bush traveled from the White House with first lady Laura Bush to greet Pope Benedict XVI after his plane landed Tuesday afternoon at Andrews Air Force Base outside Washington, D.C.
It's the first time that Bush has left the White House to greet a foreign dignitary, and the first official papal visit to the United States since the establishment of full diplomatic relations between the United States and the Vatican 24 years ago.
"Obviously, it shows the deep respect that the president has for the pope and also the recognition that there's a lot of Catholic voters out there," said Father Thomas Reese, a Jesuit and senior fellow at Georgetown University's Woodstock Theological Center.
Walking on a red carpet, the president warmly greeted the pope shaking his hand after he emerged from his plane, nicknamed Shepherd One.
As he was getting into the back of his limousine, the crowd at Andrews Air Force Base in Maryland sang a few bars of "Happy Birthday" to the pope, who turns 81 on Wednesday.
Bush: Pope Is Worldwide Spiritual Leader
ABC News contributor Cokie Roberts was invited to ride with the president, the first lady, and first daughter Jenna Bush, for his unprecedented trip from the White House to greet the pope at a military base in Maryland.
"The president said the pope is a worldwide spiritual leader and that millions of American citizens are excited about having him in this country and that he, the president, wanted to go to Andrews Air Force Base as a sign of respect," said Roberts, whose mother, Rep. Lindy Boggs, D-La., was the U.S. ambassador to the Vatican from 1997 to 2001.
"He said the pope is major figure in the world and more people listen to him than anyone else in the world," Roberts said.
Bush Cozies Up to Pope
This is Benedict's first visit to the United States, and the first chance for many Americans to get an up-close view of the man who succeeded the charismatic and popular late Pope John Paul II. Benedict has won praise from religious scholars for his emphasis on the marriage between faith and reason.
Benedict has denounced terrorism as a separation of religion and reason.
Pope to Address U.N.
During his six-day visit to the United States, the pope will address the United Nations on the 60th anniversary of the UN declaration on human rights.
Both he and his predecessor publicly denounced the president's decision to wage war unilaterally against Iraq. The pope is expected to call for a diplomatic and political solution rather than a military solution to the violence in Iraq that has left Christian minorities there vulnerable.
"I think the pope will be pretty diplomatic," Reese said. "He's not going to wag his finger at the president, even though he has disagreed with him. ... He's not going to stand on the White House lawn and say, 'Pull the troops out immediately.'"
Bush will host Benedict Wednesday for a private 45-minute meeting in the Oval Office after an elaborate official arrival ceremony with more than 9,000 invited guests expected on the South Lawn, more than were present for the arrival ceremony for Queen Elizabeth II last May.
During his visit the pope will drive his Popemobile down Pennsylvania Avenue and visit with Bush in the Oval Office. The president, giving the pope an especially lavish welcome, will also entertain the pope's entourage and special guests at a special White House dinner Wednesday night in the East Room of the White House -- though Benedict will not be there. As Vatican officials point out, popes traditionally never attend state dinners.
Benedict will also visit ground zero in New York and celebrate two stadium masses -- one in Nationals Stadium in Washington and one in the soon-to-be-demolished legendary home of the New York Yankees.
In an interview last week with a Catholic news outlet, Bush explained the reasons for the grand papal welcome.
"I subscribe to his notion that there's right and wrong in life, that moral relativism has a danger of undermining the capacity to have more hopeful and free societies," Bush told the Eternal Word Television Network. "I want to honor his convictions."
'Deeply Ashamed' Over Sexual Abuse
On the flight to the United States Tuesday, Pope Benedict XVI said he was "deeply ashamed" over the sexual abuse scandal that has swept the U.S. Catholic church since 2002, provoking lawsuits that have forced churches to pay more than $2 billion in settlements and shaken the faith of many Catholics here.
"We will absolutely exclude pedophiles from the sacred ministry," he said.
About 75 percent of Catholics in the United States disapprove of the Catholic church's handling of the sexual abuse scandal, according to a recent ABC News poll.
Abuse victims in the United States accused the pope of shielding some 19 bishops who have been accused of sexual abuse.
When asked whether the pope and the president will discuss the sexual abuse scandal, White House Press Secretary Dana Perino said Tuesday," I won't rule it out, but I don't necessarily think it's necessarily on the president's top priorities."
Perino said Bush will focus on "their shared values of human rights and the importance of fighting extremism, and also promoting religious tolerance especially when there are religious minorities in countries."
Religious scholars said Bush may not wish to highlight anger in the U.S. over the sexual abuse scandal.
"The president doesn't want to get involved in the internal matters of the church, just as the pope wouldn't want to be seen to be interfering with the politics of this country," said John Green, senior fellow in religion and American politics at the Pew Forum on Religion & Public Life.
Bush, Pope at Odds on International Issues
Bush first met Benedict last June during a visit to the Vatican, where they discussed religious persecution in China, and AIDS in Africa.
While Bush and Benedict generally agree on their opposition to abortion rights, gay marriage and stem cell research, there are far more areas where they disagree.
"There are many areas in terms of international relations where the pope and the president are not on the same page," Reese said. "It's true that they both oppose abortion, but once you get off that topic, they're pretty much in different places."
The Vatican has spoken out against the death penalty, which Bush supports, and has called the U.S. embargo against Cuba "immoral." Benedict and Bush also disagree about the urgency of environmental issues, especially the dangers of global warming, and how much government support the poor should receive.
"The pope is also much more supportive of multinational institutions, [such as] the U.N.," Reese said. " He doesn't think that individual nations should just try to exercise their power independent of what the rest of the world is doing."
Most Americans Like the Pope
While U.S. Catholics feel increasingly conflicted about their faith, an overwhelming majority of Americans hold a favorable view of the pope -- 74 percent express a favorable impression of him overall, according to an ABC News poll released this week. That compares with 87 percent for his long-serving predecessor, Pope John Paul II, in 2005.
"His personality is so different from that of John Paul II, who was a bigger than life charismatic that dominated the world's stage," Reese said. "Benedict is more reticent, shy, a scholar, a professor type, but I think he has a very warm and engaging smile. He is very personable when he interacts with people, and so I think people will warm up to him during his visit."
The pope raised the ire of Muslims in a university speech he made in Germany in 2006 when he cited a medieval Byzantine emperor who had called the Prophet Mohammed "evil and inhuman."
Bush, a Protestant, has taken pains during his presidency to identify with religious voters, including American Catholics, who account for nearly 25 percent of U.S. adults, according to a study recently released by the Pew Forum on Religion and Public Life. About 51 percent of Americans are Protestant, and about 16 percent say they are unaffiliated with any religion.
Since his 2000 presidential campaign, Bush has focused on courting Catholic voters and wooing them away from the Democratic Party, touting his "compassionate conservatism" and his opposition to abortion, gay marriage and stem cell research, which is in line with the teachings of the Catholic church. In 2004, more Catholics identified themselves as Republican than Democrat for the first time in exit polls dating back to 1972. However, those GOP gains were quickly wiped away in the 2006 midterm election.
The White House and the Holy See
In the decades before the current Bush Administration, the White House and the Holy See were often seen as allies in international politics.
In 1939, President Franklin Roosevelt sent a personal representative to the Vatican to keep an eye on fascist Italy. The U.S. president and Pope Pius XII entered into an anti-communist alliance between the Holy See and the White House that lasted throughout the Cold War.
However, fearing a Protestant backlash, a U.S. ambassador wasn't sent to the Vatican until 1984. President John F. Kennedy, the only Catholic U.S. president, reassured Americans in a famous speech that his presidency would not be beholden to the pope.
In 1984, President Ronald Reagan upgraded the U.S. representative to the Vatican to rank of ambassador, partly in recognition of Pope John Paul's staunch nonviolent opposition to Soviet communist rule in Eastern Europe.
This is the 25th visit between a sitting U.S. president and a pope.
Former ABC News Rome bureau chief Bill Blakemore covered Pope John Paul "from balcony to grave" and traveled with him on many of his trips abroad. ABC News' Ursula Fahy and Gary Langer contributed to this report.