Obama speaks vividly of his decision more than 20 years ago to become an active, church-going Christian.
"Kneeling beneath that cross on the South Side, I felt that I heard God's spirit beckoning me,” he said in a speech last year in Hartford, Connecticut.
"I submitted myself to His will, and dedicated myself to discovering His truth."
Obama's frequent invocation of his religion makes him unusual among Democrats, who tend to be more secular than Republicans.
Democratic candidates usually support abortion rights, women's rights, and gay marriage, and oppose the mixing of state and church, for example, on the issue of allowing officially sanctioned prayer in public school classrooms.
"For the last several elections it's really been the Republican candidates, particularly George Bush, who have talked extensively and comfortably about their faith," says John C Green, an expert on the politics of religion in the United States at the University of Akron, Ohio.
"The Democrats were somewhat reticent. This year it seems to be exactly the opposite."
'Muslim' accusations
One reason Obama may talk often about his Christian beliefs is to convince voters he is not secretly a practicing Muslim.
A concerted campaign spread via the internet and word of mouth seeks to portray Obama as an adherent of Islam.
These assertions are meant to damage Obama among unsophisticated or poorly educated voters who harbour prejudice against Muslims.
"Most Americans tell us in polls that they would not be comfortable voting for an Islamic candidate for president," Green says.
"There are other groups that people wouldn't feel comfortable voting for as well so, to the extent some Americans believe that senator Obama is a Muslim or of Muslim background, that could create a problem."
While Obama discusses his relationship with Jesus without hesitation, Republican John McCain appears uncomfortable talking about religion — his or anyone else's.
"Senator Obama talks very comfortably about his faith," Green says.
"He's very interested in pursuing religious voters. John McCain is little bit stand-offish. He's not that happy and that comfortable talking about that subject."
McCain's television ads and campaign speeches hardly ever mention Christianity, with one exception: a Christmas story about a kindly Vietnamese prison guard.
"One night, after being mistreated as a POW, a guard loosened the ropes binding me, easing my pain," McCain says, in a campaign TV ad.
"On Christmas, that same guard approached me, and without saying a word, he drew a cross in the sand. We stood wordlessly looking at the cross, remembering the true light of Christmas.
"I will never forget that no matter where you are, no matter how difficult the circumstances, there will always be someone who will pick you up."
Key voting block
George Bush, the current president, made prayerful appeals to fellow evangelical Protestants the cornerstone of his winning electoral strategy.
 |
John McCain has failed to inspire
evangelical voters [AFP] |
Evangelicals represent about 23 per cent of the electorate, according to studies by the Pew Research Center.
Seventy-eight per cent of evangelicals supported Bush in 2004, giving him the margin of victory he needed to edge out Democratic rival John Kerry in key states, especially Ohio (remember that Bush actually lost the popular vote in the 2000 election by about half a million votes).
Now Obama wants to bring some of that evangelical flock into his tent.
"We have to remember that the 2004 election was very, very close," Green says.
"If we had an election that was that close again, just a small shift in these voting blocks could make a difference.
"So, Senator Obama does not need to win a majority of the white evangelical vote. If he could do as much as 30 per cent of that vote, all other things being equal, he could be in pretty good shape to win the White House."
While the majority of conservative, Evangelical voters are likely to choose McCain, he is not personally popular among them.
"There's a real lack of enthusiasm for him personally," Green says.
"Senator McCain has certainly not lost the evangelical vote, but he's having some trouble getting the same level of support president Bush has and ... he may not be able to do that, simply because he doesn’t have the kind of tie to the evangelical community that George Bush has."
Controversial pastors
McCain's ties with evangelicals were hurt when he was forced to repudiate two prominent pastors who supported him.
He rejected Ohio's Rod Parsley because of his anti-Muslim preachings, and Texan John Hagee after he implied the Nazi Holocaust was part of God's plan for the Jewish people.
 |
Obama faced criticism over his
association with Jeremiah Wright [EPA] |
Obama also got into pastor trouble when the sermons of his long-serving minister Jeremiah Wright were criticised as racially inflammatory and unpatriotic.
But Protestant evangelicals are not the only religious group which matters, Green says.
"There has been a tendency to overstate the influence of evangelical voters.
"This is a very important group, but it is not the determinative group in American politics."
Jewish voters, concentrated in key states like Florida and Pennsylvania, normally vote Democratic, but they are not sold on Obama.
"There is still a great deal of unease among Jewish voters with regard to senator Obama," Green says.
"Some of it has to do with his foreign policy issues, where they're not sure how strong a friend he is of Israel - despite the fact that he has, of course, argued that he really is."
And blue-collar Catholic voters, concentrated in critical swing states like Ohio, Michigan and Pennsylvania - could be the most crucial group of all.
Polling shows many white, working-class Catholic voters are fed up with Bush and inclined to vote Democratic.
But, in the Democratic primaries, they supported Hillary Clinton over Obama —many citing Obama's lack of experience as the reason.
Now, McCain is hoping he can attract a sufficient number of Catholic voters to win in those key states.
If he can win them, he might also win the White House.