Both are from modestly sized cities in Indiana. Both were baptised Catholic but came to embrace other branches of Christianity. Both found inspiration in former president John F Kennedy as they launched political careers of their own.

The parallels between Mike Pence and Pete Buttigieg stop there.

The Republican vice-president, 59, who is opposed to gay marriage, and the 37-year-old Democratic presidential candidate, who is married to a man, have found themselves at opposite ends of a debate about homosexuality, religion and tolerance.

They have also become avatars of a struggle between the Christian right, which has long sought to claim a monopoly on morality, and a resurgent Christian left preaching inclusiveness and social justice. For Indiana, and America, they offer radically different readings of the Bible and how it should inform 21st-century politics.

Push come to shove, he can abandon his religious and moral principles for political reasons Buttigieg on Pence

Should Buttigieg – who raised $7m in the first quarter, raced up the polls and formally launches his White House campaign on Sunday – fall short in the primary but be chosen as the eventual nominee’s running mate, the world views would collide in a blockbuster vice-presidential debate between two “Hoosiers”, as Indianans are known.

“If me being gay was a choice, it was a choice that was made far, far above my pay grade,” Buttigieg said by way of a preview at a recent LGBT event, where even atheists were impressed. “And that’s the thing I wish the Mike Pences of the world would understand: that if you’ve got a problem with who I am, your problem is not with me. Your quarrel, sir, is with my creator.”

A crucifix is on display at the Saint Bartholomew Catholic parish. Photograph: Alyssa Schukar/The Guardian

Both men are products of America’s church-heavy heartland. Early Indiana attracted French Jesuit missionaries, Quakers and German, Irish and eastern European Catholics. “The southern immigrants who moulded Hoosier society brought a deep, fundamentalist faith, a passion for fiery oratory, and a mistrust of authority,” records the state museum in the capital, Indianapolis. “Evangelical Protestantism profoundly shaped their conservative outlook, and thus shaped Indiana attitudes and politics.”

Pence’s Irish Catholic grandfather came through Ellis Island, moved to Chicago and worked as a bus driver for 40 years. The family revered Kennedy, America’s first Irish-Catholic president, and voted Democratic. Born in Columbus, Pence and his brothers were altar boys at their Catholic church and went to its affiliated school.

But later, when he was at university, Pence came to yearn for a greater intimacy with God. He found it in evangelical Christianity. Charles Hiltunen, 57, who was a fellow law student, recalled: “I think it was the spirit that grabbed him in the evangelical setting. He’s very energetic and lives the Word and I think that fulfilled his appetite. He still has his roots in the Catholic faith, but I think that’s his energy.”

Pence is the only one of six siblings no longer part of the Catholic church. The Rev Clement Davis, the priest at the Columbus church where Pence was baptised, has said this transition disappointed his mother. “You could see Nancy just shake her head about it,” he told the New York Times in 2016. “She was disappointed. She had hoped he could find his way back to the church.”

This week at the church, Patrick McKinney, 51, a construction project manager whose wife planned one of Pence’s children’s weddings, expressed support for the vice-president’s views about gay marriage.

“The natural part of marriage is bringing children into the world,” he said. “It can’t be replicated with the same sex. This is not being critical of other people: God loves us all the same.”

Patrick McKinney, a construction project manager, takes measurements for an update to the Saint Bartholomew Catholic parish. Photograph: Alyssa Schukar/The Guardian

As a born again Christian, Pence carved a reputation as one of the most socially conservative congressmen, then governors, in the country. His selection by Donald Trump as running mate is now seen by many as a political masterstroke that helped reassure and mobilise sceptical Christian evangelicals to support the unconventional Republican nominee.

Pence has remained ostentatiously loyal – some say obsequious – even as his boss tramples on norms, hurls profane and vulgar insults and faces accusations that he authorised hush money payments to a pornographic actor and Playboy model during the 2016 campaign. Pence’s motive in continuing to defend Trump’s profoundly un-Christian behaviour remains one of the great enigmas of the age.

The vice-president’s friends and supporters find no contradiction. Mike Murphy, a Republican politician and strategist in Indiana, said: “He has a blind devotion to the idea God has a plan for everybody. The fact Donald Trump asked him to be his running mate, he thinks, is part of God’s plan and not violating his Christian faith at all. I’m sure he thinks he is mitigating Trump to some extent.”

Hiltunen, a principal at the lobbying firm Sextons Creek, suggests Trump and Pence’s odd couple relationship is mutually beneficial.

“I’ve heard people say he’s a hypocrite but I actually think it makes him even stronger that he is able to work in that environment. If you see the president before Mike Pence and you see him now, you can see that he has had some kind of impact on him. Maybe he sees it as a work in progress … He is the exact opposite and maybe that’s why it works.”

A pedestrian passes through downtown Columbus. Photograph: Alyssa Schukar/for The Guardian

In Indiana and beyond, progressives take an altogether different view. Many say Pence has made a career out of attacking LGBT rights and has led Christian evangelicals into becoming apologists for the most destructive president of modern times. No one is more puzzled about his continued defence of Trump’s un-Christian conduct than Buttigieg.

In a February interview with the Guardian in South Bend, where he has been mayor since 2012, he said: “There are two competing accounts of what this means. One is that it means, push come to shove, he can abandon his religious and moral principles for political reasons and just team up with this guy who at least theoretically goes against everything he stands for.

“The other theory that’s been floated is that he has some bizarre theological sense of destiny that even this is part of some divine calling, that for some weird reason God wants him to team up with a corrupt, philandering megalomaniac for the greater good of the kingdom. I don’t know which of those is more worrisome. I don’t know which of those is true.”

Pete Buttigieg, in front of the county courthouse in South Bend. Photograph: Lucy Hewett/The Guardian

‘The scripture is about protecting the stranger’

Buttigieg presents a very different vision of Christianity. Bidding to become America’s youngest and first openly gay president, he has spoken as freely about his faith as he has about his sexuality, further distinguishing himself in a party that, he argues, has lost touch with its religious traditions and ceded too much territory to Republicans.

“The scripture is about protecting the stranger, the prisoner, the poor person, and that idea of welcome,” he said at a CNN town hall. “That’s what I get in the gospel when I’m in church.”

Buttigieg’s father, a Maltese immigrant, was a Jesuit who became a secular intellectual, while his mother identified as Anglican. Their son, who has Kennedy’s inaugural address framed above his desk, went to a Catholic school but did not have a religious awakening until he reached Oxford on a Rhodes scholarship. Returning to South Bend, he found his spiritual home in the Episcopal church.

He knows better. He knows me Pence on Buttigieg

Buttigieg married his husband, Chasten, in a church service last year. He has said he believes the marriage moved him closer to God. More than half a century since Martin Luther King Jr’s faith-driven push for civil rights, the military veteran appears willing to scramble fault lines and take on the Christian right on its own terms.

Fate ensured that Governor Pence and Mayor Buttigieg’s paths would cross in Indiana and over four years the pair had cordial dealings on economic development, touring factories together and reportedly exchanging texts. Pence lavished Buttigieg with praise, calling him “energetic, innovative, forward-looking, creative”. Buttigieg even presented Pence with a South Bend promotional T-shirt that said “I (heart) SB”.

Mike Pence speaks to Pete Buttigieg following a Dyngus Day event in South Bend, Indiana, in 2013. Photograph: Robert Franklin/AP

In an interview with CNBC this week, Pence said they had a “great working relationship” and seemed dismayed by the mayor’s recent characterisation of his religious beliefs.

“He knows better,” Pence said. “He knows me.”

Hiltunen recalled: “They respected each other and actually liked each other. I think Pete came out once and said, ‘Mike Pence is a great guy.’ He got beat up for it. It’s not only the Christian roots, it’s the Hoosier roots. Indiana is a very small place, whether you’re from Columbus or South Bend. Everybody’s a step removed from one another.”

But Buttigieg did condemn Pence’s controversial support for legislation that made it easier for religious conservatives to refuse service to gay couples, citing it as a factor in his decision to come out in 2015. And since entering the presidential race, Buttigieg has sharpened his rhetoric and become less conciliatory towards the Pence.

He told the Guardian earlier this year: “The bottom line with him is he really believes all this stuff and he’s said so. I don’t know if he believes in evolution. I think he believes people decide to be gay. He’s written down that cigarettes don’t kill. Science and evidence are just not a big part of how he comes at the world.

“He was not a very effective governor. I’m on my third Republican governor now and the other two, his predecessor and his successor, were considered effective enough that they also commanded grudging respect from Democrats. With Pence it’s kind of the reverse.”

Vice-President Michael Pence is known to attend College Park church in Carmel, Indiana. Photograph: Alyssa Schukar/The Guardian

Buttigieg acknowledged: “We did work together on some things. I wrote in my book about an economic development initiative that I teamed up with them on that I thought was very good policy but, for the most part, even Republicans didn’t have a lot of respect for the office once they saw how it was run on his watch.”

Old friends of Pence defend his record as governor and insist they do not recognise the popular image of him as a zealous, homophobic puritan who might have wandered out of Arthur Miller’s play The Crucible. They describe him as a midwestern pragmatist, laud his sense of humor and are eager to point out that, when Pence’s son married, the best man, named Henry, was gay.

Curt Smith, president of the Indiana Family Institute and an opponent of same-sex marriage, said of Buttigieg: “I wish he would stop attacking the vice-president’s faith. I think that’s dangerous. But I welcome this conversation about the so-called Christian left.

“It’s not a very active force in American public life and I think he could make a major contribution to the discourse in our country … I’d love to open the scriptures and do moral reasoning with people on the other side of the aisle. There hasn’t been anyone to talk to for a very long time.”

Don and Abbajean Graf walk through Columbus visiting from their home in Bloomington. Photograph: Alyssa Schukar/The Guardian

‘Different faithful people have a different God in mind’

Christians of all political stripes coexist in Columbus, which is Pence’s birthplace, a celebrated playground for modernist architects about to host its second gay pride festival.

Pence family friend Chris Donica, 44, a sales assistant working on the pretty main street, said: “There are a lot of Christian values in this town. I lived in Sweden for a while and it was too liberal: there were a lot of things, like nudity on the beach, I would never see here. God comes first here and Mike Pence has very good Christian values. Once he says he’s going to do something, he follows through with it.”

Don Graf, 82, a retired businessman out walking with his wife of 60 years, said: “The Bible says marriage is between a man and a woman. I’m not aware of any church that condones gay marriage. Any Bible-based church would not be in favour of it because it’s biblically unsound.”

Should Buttigieg become president, however, Graf said he would have to accept the idea of a first gentleman in the White House. “I wouldn’t like it but the Bible says you have to support whoever is in office.”

Beth Stroh, owner of Viewpoint Books in downtown Columbus, Indiana. Photograph: Alyssa Schukar/The Guardian

In Viewpoint Books, titles including A Day in the Life of Marlon Bundo, a satirical book about Pence’s pet rabbit having a gay romance, are on display. Beth Stroh, 62, the owner, said: “I think different faithful people probably have a different God in mind and I am more welcoming to the less judgmental and more loving God, so my personal view would be more aligned with Pete.”

It is no surprise, she added, that amid the country’s current echo chambers, people interpret the Bible in different ways. “In 2019 we tend to find alignments that are comforting for us and there is perhaps less willingness to look at other views. That’s part of the polarisation we’ve all identified as happening. People like to find their place and then find support for that position.”

Across Indiana, many Christians hope Buttigieg will prompt new conversations and mutual understanding. Jon Hodge, 30, area coordinator of the National Network of Youth Ministries, said: “There is a really interesting sense in the church that if somebody’s a Republican they’ve been told they’re not Christian, and the same is true on the other side: if somebody’s a Democrat, they’re not Christian.

“We as a church need to be about reconciliation. We need to reconcile our differences with each other. Jesus came to Earth to reconcile but sin had entered the world and created the divide. If we in the church can’t reconcile, there’s no hope.”

Others reject labels that create a false equivalence and urge a focus on the moral centre. The Rev Dr William Barber, a pastor in North Carolina and co-chair of the Poor People’s Campaign: A National Call for Moral Revival, said in a phone call: “The left versus right categorisation is not biblical. It is not a theological frame. There is no text in the Bible that talks about somebody being on the left or being on the right. That is not even orthodox Christianity.

“The overwhelming concern of God is how you treat the poor, how you treat the sick, how you treat the immigrant, how you treat women, how you treat children. So when you look at that from a theological standpoint, you then look at policy and you say, ‘Now, how does this politician’s policies line up with the overwhelming concerns of God as it relates to scripture?’”

Barber said he was encouraged by racial justice, poverty and other issues gaining greater prominence.

“We have needed a moral narrative shift for a long time because the so-called extremists hijacked the moral discussion and the only times we would talk about morality was when it pertained to women’s right to choose, prayer and LGBT issues. That is a far too limited moral conversation, particularly when you look at the real depths of moral concern of the public square in the scriptures and in the life of Jesus and in the life of the prophets.”