If there's one thing former Alaska Gov. Sarah Palin and President Obama have in common, it may just be a belief in the importance of prayer and the federal government's role in setting aside a day for it.
Today is the National Day of Prayer, required by law since 1952, when the president calls on Americans to "turn to God in prayer and meditation."
From conference rooms in government office buildings to private chapels, the steps of the U.S. Capitol and the Pentagon, thousands will gather across the country to express publicly their faith in the federally-sanctioned tradition.
But this year's observance comes as the 59-year-old practice is under fire and facing a possible ban after a federal district court last month ruled that the prayer day violates the First Amendment's Establishment Clause, which prohibits the government from imposing an official religion or showing preference to one.
The National Day of Prayer "serves no purpose but to encourage a religious exercise, making it difficult for a reasonable observer to see the statute as anything other than a religious endorsement," Judge Barbara Crabb of the U.S. District Court for the Western District of Wisconsin wrote April 15.
"No one can doubt the important role that prayer plays in the spiritual life of a believer. … However, [that doesn't mean] the government may enact a statute in support of it, any more than the government may encourage citizens to fast during the month of Ramadan, attend a synagogue, purify themselves in a sweat lodge or practice rune magic," Crabb wrote.
Enforcement of the ruling is on hold while an appeals court hears the case. The Obama administration, the respondent in the case, contends that the day is only an "acknowledgement" of the country's religious tradition.
"Prayer has been a sustaining way for many Americans of diverse faiths to express their most cherished beliefs, and thus we have long deemed it fitting and proper to publicly recognize the importance of prayer on this day," Obama wrote in his official proclamation.
The case, brought by the Freedom from Religion Foundation, a group of atheists and agnostics, now puts the administration in an uncomfortable position of defending something against the wishes of a constituency that it has tried to court as part of its commitment to pluralism and diversity.
"It is such a profound violation of conscience for Congress to direct our president to tell all citizens to pray, and that they in fact must set aside an entire day for prayer once a year," foundation president Annie Laurie Gaylor said.
Rev. Franklin Graham Prays Amid 'Day of Prayer' Controversy
Ostensibly, the National Day of Prayer endorses no specific faith or religion, but it has taken on a distinctly Christian character in recent years to which several non-Christian groups have objected.
The National Day of Prayer Task Force, a private group that coordinates thousands of events nationwide, is run by Shirley Dobson, wife of evangelical Christian conservative James Dobson, president of Focus on the Family.
Lawmakers first considered enacting a national day of prayer in 1952, largely at the behest of Christian evangelist Billy Graham, who then argued the law was necessary because the country had "dropped our pilot, the Lord Jesus Christ, and are sailing blindly on without divine chart or compass."
Graham's son, the Rev. Franklin Graham, has been at the center of controversy recently after the Pentagon disinvited him from leading and attending a National Day of Prayer event because of controversial remarks he made about Islam, which he described as "evil."
The Pentagon service is attended by mainline Protestants, Muslims and Jews.
Graham staged a small protest this morning outside the Pentagon, where he held a short prayer on an adjacent sidewalk with his wife and a few others. "As a Christian, why I can't have the same right" to say that I worship a different God than Muslims and Hindus, Graham told reporters. "It looks like Islam has gotten a pass. … We're losing our freedoms while others are getting more."
"We are fooling ourselves if we think we can have some big kumbaya service and all hold hands and it's all going to get better in this world," Graham told USA Today Wednesday. "It's not going to get better."
Still, an overwhelming majority of Americans -– 92 percent -– say they believe in God, according to the most recent USA Today-Gallup poll. Most also favor the National Day of Prayer, with only 4.5 percent opposed.
"It's a sad day in America when an atheist in Wisconsin can undermine this tradition for millions of others who simply wish to join their fellow citizens in praying for their country," the prayer task force said in a statement.
Dobson said the April court decision will be appealed on grounds of the country's heritage. "Since the days of our Founding Fathers, the government has protected and encouraged public prayer and other expressions of dependence on the Almighty," she said.
Prayer Events at U.S. Capitol, Pentagon
In the meantime, the prayer groups and bible readings will continue today under the banner of federally sanctioned Day of Prayer.
At the U.S. Capitol in Washington, D.C., hundreds of faithful and dozens of lawmakers will gather -– and more will tune in live online -- for the conclusion of a 90-hour bible reading marathon on the west terrace.
"People from across America and across the world are surprised we have the right to do this, and we do," Terry Shaffer Hall, coordinator of the U.S. Capitol Bible Reading Marathon, said of the 21-year-old tradition. "What a better place to express freedom than this. We are Americans and behind us is the peoples' house."
ABC News' Luis Martinez contributed to this report.