It's happened to John McCain and Barack Obama. Now it's Sarah Palin's turn to go through what one observer has called a "spiritual vetting."
For two decades, Palin was a member of an Assemblies of God church in her hometown of Wasilla, Alaska. In 2002, years before she was elected governor of Alaska, Palin and her family switched to a nondenominational church, but Palin still returns to her old church on special occasions.
There are an estimated 3 million worshippers in the Assemblies of God church in the Unites States, according to the Pew Forum on Religion and Public Life. Worldwide there are 500 million members, which is approximately 25 percent of all Christians. The Assemblies of God church is a form of Pentecostalism, which has become one of the fastest growing Christian movements in the world.
The most scrutinized and least understood aspect of the Assemblies of God Church and Pentecostalism in general is the ancient practice of "speaking in tongues."
"Speaking in tongues is a heavenly language," said Donna Morgan, a member of the Pennsylvania-based Freedom Valley Worship Center who embraces the experience. "That we're going to God and Jesus intercedes for us."
"It's almost as if I'm able to tap into God's heart and what he wants," said Amber Crone, who is also a member of the Freedom Valley Worship Center.
Pentecostalism has been described as evangelical experience on steroids. Like evangelicals, Pentecostals believe that the Bible is the literal word of God and that the end of time is near. However, Pentecostals also believe that the Holy Spirit can give you gifts such as speaking in tongues, prophesy, and divine healing.
"It's very common in Pentecostal churches to be emotionally involved, physically involved in our worship service," Palin's former pastor Tim McGraw said. "And the reason for that is that if you go to a football game and your team wins or kicks a field goal to win it's entirely consistent to be happy."
Other Christians have sometimes derided Pentecostals as "holy rollers," which may explain the defensiveness ABC News found when visiting an Assemblies of God Church in New Jersey this weekend.
"A lot of people have their opinions about charismatic people. OK. They're called a bunch of names, but you see I tell people all the time, 'You can't knock something if you haven't walked into it. You can't knock something unless you've tried it,'" said Pastor Michael Kelly of the Riverside Assembly of God Church in Jersey City.
As America gets a crash course in Sarah Palin, the question has been raised of how her two decades as a member of the Assemblies of God church in Wasilla has shaped her personality. If elected, Sarah Palin would become the most powerful Pentecostal in U.S. history. So how has this church shaped her as a leader?
"Sarah Palin, if she was just a plain Evangelical woman, would have a tough time thinking that she could be VP," said University of Rochester religion professor Anthea Butler. "An evangelical woman might have issues with submission. What's gonna happen with my kids? But a Pentecostal woman is saying God is calling me, I'm gonna answer this call."
In a video of Palin speaking at her former church after she had become governor, she talks about the war in Iraq and a gas pipeline in terms of god's will. This is a common notion for Pentecostals who believe god regularly intervenes in human affairs.