The mayor said the governor struck him as “affable, even gentle.”

The governor called the mayor “energetic, innovative, forward-looking, creative.”

What went awry between Democrat Pete Buttigieg, the gay mayor of South Bend, Ind., and White House aspirant, and Mike Pence, once the state’s Republican governor and now the country’s vice president?

Everything, says Buttigieg, who is trying to unseat President Trump, along with 17 other Democratic candidates, and is taking aim at Pence in the process. (The mayor is expected to announce a formal candidacy on Sunday.)

Nothing, says Pence, who is trying to ensure another term in Washington as Trump’s No. 2.

“He said some things that are critical of my Christian faith and about me personally, and he knows better,” Pence said in an interview with Joe Kernen on CNBC’s “Squawk Box” set to air on Thursday morning. “He knows me.”

“We had a great working relationship,” Pence, the former governor and congressman, said of their time working together in the Hoosier State, suggesting that the criticism was part of Buttigieg’s effort to distinguish himself in a crowded Democratic field.

The contest between the two men — always personal opposites, once uneasy partners and now clearly adversaries — is one of the starkest of the 2020 campaign season. It could be a defining feud of the election, especially if the millennial Democrat falls short of his ultimate aspiration but nonetheless joins the Democratic nominee as a running mate. In that case, he would meet Pence on the debate stage.

Buttigieg is playing up their differences in his now not-so-long-shot bid for the Democratic nomination. The 37-year-old mayor and Afghanistan war veteran surged to third place in a poll of New Hampshire voters released Wednesday by the Saint Anselm College Survey Center.

As he rises from relative obscurity, the young mayor is putting a target on the back of his fellow Hoosier. He calls the vice president “fanatical” — a “social extremist” and a “cheerleader of the porn star presidency.” In a speech at the LGBTQ Victory Fund’s National Champagne Brunch on Sunday , he cast his coming-out story as a parable of what he said religious conservatives miss when they oppose same-sex marriage.

He had one particular religious conservative in mind. “And yes, Mr. Vice President,” he affirmed when discussing his marriage to another man. “It has moved me closer to God.”

“That’s the thing I wish the Mike Pences of the world would understand: That if you have a problem with who I am, your quarrel is not with me,” Buttigieg said. “Your quarrel, sir, is with my creator.” His speech turned Pence into a trending topic on social media.

The candidate’s broadsides against the vice president have endeared him to Democrats, and to the LGBTQ community in particular, which has helped bankroll his campaign. He raised $7 million in the first quarter of 2019, an impressive haul for someone who recently enjoyed little national name recognition and was hardly guaranteed to participate in the Democratic National Committee’s June and July debates. In the quest to score points against Trump and Pence, who are loathed by the Democratic base, Buttigieg has a particular vantage point from which to attack.

At the same time, a battle with the former Republican governor of his home state could undercut the mayor’s argument that he is best-suited for the general election because he is a successful Democrat in a red state. Already, his criticism of Pence is prompting harsh responses from conservatives. The evangelical commentator Erick Erickson questioned whether Buttigieg, an Episcopalian, is a true Christian.

Buttigieg is seeking to thread the needle by speaking of a resurgent religious left. He argues that Democrats should embrace discussion of faith and values central to voters in his home state, which former president Barack Obama won in 2008 — the first Democrat to do so in nearly a half-century.

In his book, “Shortest Way Home: One Mayor’s Challenge and a Model for America’s Future,” Buttigieg recalled how he had associated the most hard-line faction of Indiana politics with Pence’s record in Congress as a “conservative warrior.” He was surprised, then, to learn that Pence was personally gracious when they met for the first time at a 2011 event at the Indianapolis Motor Speedway, the mayor wrote.

At Pence’s inauguration in 2013, Buttigieg told him that he was keen to work with him. The freshly minted governor nodded and agreed, “and a long and complicated relationship began,” Buttigieg wrote in the book, which came out earlier this year.

He praised Pence for his “visionary economic development effort,” which lifted South Bend, according to the mayor. And he recounted how the then-governor called him in 2014 to express his admiration as the lieutenant in the Navy Reserve prepared to deploy to Afghanistan.

But then he watched as Pence defended Indiana’s 2015 Religious Freedom Restoration Act, which allows businesses to cite religious reasons for refusing to serve customers — a measure that critics see as anti-gay.

After seeing Pence duck a question on ABC’s “This Week” in March 2015 about discrimination against the LGBTQ community, Buttigieg strained to “reconcile what I had just seen on-screen with the Mike Pence I knew, a man who had always been gracious and decent to me in person,” he wrote.

As the controversy over the legislation unfolded, dividing Indiana, the mayor made a decision while campaigning for reelection. In a 2015 op-ed in his hometown newspaper, the South Bend Tribune, he disclosed his sexuality and wrote that the “disastrous ‘Religious Freedom Restoration Act’ episode” had created an opportunity to “demonstrate how a traditional, religious state like ours can move forward.”

“If different sides steer clear of name-calling and fearmongering, we can navigate these issues based on what is best about Indiana: values like respect, decency, and support for families — all families,” he wrote in the piece, which does not mention Pence.

Pence, for his part, appeared to continue to hold Buttigieg in high regard.

When he visited South Bend in 2016 to break ground on a major redevelopment project, Pence singled out the town’s mayor for praise.

“South Bend, Indiana, is so blessed to have an energetic, innovative, forward-looking, creative mayor in Pete Buttigieg,” he said.

Two months later, Pence joined the Republican ticket as Trump’s running mate. According to a 2017 profile of Pence in the New Yorker, Trump had once joked that his No. 2 wanted to “hang” gay people. A spokeswoman for Pence called the claims “untrue and offensive.”

Defending his criticism of Pence, Buttigieg argues that a gulf separates how the vice president acts from what he believes and advocates.

When Stephen Colbert asked him in February if the vice president was a “good guy,” Buttigieg demurred.

“He’s nice. If he were here, you would think he’s a nice guy to your face,” the mayor said. “But he’s also fanatical.”

The candidate reiterated that point this week, in an apparent response to a move by the vice president’s aides to recirculate Pence’s praise of him.

Karen Pence, the vice president’s wife, also objected to Buttigieg’s comments.

“They’ve always had a great relationship,” the second lady, who is teaching at a Christian school that bars gay students and requires employees to affirm their belief in heterosexual marriage, said on Fox News host Brian Kilmeade’s radio show on Tuesday. “It’s funny because I don’t think the vice president does have a problem with him, but I think it’s helping Pete to get some notoriety by saying that about the vice president.”

In Pence’s telling, and that of his wife, he has no problem with the mayor.

But the mayor says he had a problem living in Pence’s Indiana — and now, he has a problem living in the vice president’s America. That became clearer to him when he came out.

"Coming out was supposed to be a personal hurdle for me to clear, not a political statement, but doing so now meant it would be even more freighted with the complications of being openly gay in Mike Pence’s Indiana,” he wrote in his memoir.