The 30-year-old White House aide plays down his influence on his boss.

"He has always been on a Christian journey," DuBois says of Obama, "and the challenges of the office, of being leader of the free world, provides a deepening and strengthening of faith, and that's what you see with the president."

"I remember working with him around the Scripture he would use at the memorial service for the miners in West Virginia," DuBois says, referring to the 2010 tragedy that left 29 dead. "These are obviously moments when one's faith is strengthened."

The unparalleled trials of the Oval Office have been known to deepen the religiosity of presidents ranging from Abraham Lincoln to Ronald Reagan.

Hunter says the same thing has happened to this president: "His faith has been growing as the challenges of the presidency have become more naturally the main part of his own everyday life."

One of Hunter's first Oval Office encounters with Obama came shortly after the president took office, at a time when the economy was shedding 750,000 jobs a month.

"He acknowledged at that meeting what many may know but few remember: that by the time issues get to the president, there are no simple or clear answers or they would have been solved by others," Hunter says. "So we prayed."

A few months later, Hunter was in the Oval Office again, noticing that "the unremitting heaviness of the office was setting in."

"I saw something that has been consistent ever since: He cannot just pray for himself and his family," Hunter says by e-mail. "At least I have never seen it. His faith, his heart, always includes those who are being left out through no fault of their own."

Despite the changes they've seen in Obama, both Hunter and DuBois are uncomfortable with the word "transformation" when it comes to Obama's White House faith life.

"The president doesn't deal in labels," says DuBois. "He knows God's grace is sufficient for him and beyond that doesn't get into labels, evangelical or mainline. He's a proud Christian."

Loving God by loving your neighbor

When the Rev. Sharon Watkins and a group of fellow Protestant ministers sat down with Obama at the White House a couple years into the president's term, she knew the pastors would get wonky about religion.

"You get a bunch of ministers in the room and we're all church geeks -- it's theological," says Watkins, who along with the other pastors had come to talk about poverty. "But the president got every biblical allusion and reference. ... He's just a person who is biblically and theologically literate."

If Obama's personal theology has grown more conservative, he is inclined to apply it toward liberal political ends.

"I'd be remiss if my values were limited to personal moments of prayer or private conversations with pastors or friends," Obama said at the National Prayer Breakfast in February. "So instead, I must try -- imperfectly, but I must try -- to make sure those values motivate me as one leader of this great nation."

In signing laws that have increased Wall Street regulations and stopped health insurance companies from rejecting patients with preexisting conditions, Obama said at the breakfast, he wanted to "make the economy stronger for everybody."

"But I also do it because I know that far too many neighbors in our country have been hurt and treated unfairly over the last few years," he continued. "And I believe in God's command to 'love thy neighbor as thyself.'"

Obama went on to frame decisions as disparate as ending tax breaks for the wealthy and defending foreign aid as examples of biblical principles in action, quoting Jesus' teaching that "for unto whom much is given, much shall be required" and invoking the "biblical call to care for the least of these."

That last biblical reference also loomed large in another 2011 White House meeting between Obama and a group of religious leaders. They'd come to urge the president to protect programs for the poor amid his fight with Congress over raising the nation's debt ceiling.

The Rev. Jim Wallis, a progressive activist, recalls the meeting:

In pressing Obama to take cuts to those programs off the table, one Roman Catholic bishop told the president that "the text that we are obliged to obey does not say 'as you have done to the middle class you have done to me.'"

"It says as you've done to the least of these, you have done to me," the bishop said.

"I know that text," Obama responded. The passage is from the Matthew 25 in the New Testament.

"So there was this very rigorous conversation," Wallis says, "and we pressed him on applying Matthew 25 to this decision about protecting those who were the least of these."