Concord, New Hampshire (CNN) Two decades ago, Pete Buttigieg composed a nearly 1,000-word tribute to Bernie Sanders .

He spoke glowingly of Sanders' candor and conviction in an essay that would earn the teenager top honors in an essay contest.

Flash forward to 2020, and Buttigieg is locked in a tense primary fight with the man he once praised. Sanders has refocused some of his attacks on the former mayor, the latest business-friendly, moderate stand-in for the political establishment, while Buttigieg now finds himself in the awkward position of lobbing grenades at the Vermont senator.

In the crowded field of Democratic candidates, it's a rivalry neither of them expected.

Sanders spent most of January homed in on Joe Biden , hammering the former vice president over his record on social security, foreign policy and trade. And, for his part, Buttigieg targeted Elizabeth Warren throughout the fall, even at one point saying that he was in a two-way race with her in Iowa.

But the dust and delegates have settled in Iowa, leaving Warren and Biden in third and fourth place, respectively, and Sanders and Buttigieg in a virtual tie at the top. Polls now show the Vermont senator and the former South Bend, Indiana, mayor heading into Tuesday's primary in New Hampshire as the favorites.

This rapid reordering of the primary's top tier has forced Sanders and Buttigieg to redirect. Sanders has pointed to Buttigieg's wealthy donors, while Buttigieg has questioned Sanders' ability to help downballot candidates and unite the party.

Despite the recent lash of pointed rhetoric, Sanders and Buttigieg still feel like accidental rivals.

Sanders turns from Biden to Buttigieg

Sanders, I-Vt., speaks at the McIntyre-Shaheen 100 Club Dinner, Saturday, February 8, in Manchester, New Hampshire.

Since Iowa, Sanders has largely ignored Biden and trained his fire on Buttigieg, whose billionaire donors have become an instant staple of his stump speech.

The initial wallop came on Friday morning, at a Politics and Eggs breakfast in Manchester, where Sanders read off a series of headlines heralding Buttigieg's popularity with billionaire donors. Later in the day, aides passed around pieces of paper with a mashup of the stories -- including one from Forbes that read, "Pete Buttigieg has most exclusive billionaire donors than any Democrat."

In the past week, Buttigieg has thrown elbows too, stamping Sanders as a hypocrite --- in fundraising emails and text messages to supporters -- for accepting the support of "dark money groups," including the organization Sanders formed after the 2016 primary, Our Revolution.

"I like Pete. He is a smart guy. He is a nice guy," Sanders said on Sunday in Dover. "But if you are serious about political change in America, that change is not gonna be coming from somebody who gets a lot of money from the CEOs of the pharmaceutical industry. No one really believes that you're gonna take on the pharmaceutical industry when they give you massive amounts of money."

Buttigieg responded during Friday night's debate.

"I have been very clear on both my record, where I have sued pharmaceutical companies, and what I'm campaigning for, that includes raising wages and raising taxes on corporations and the wealthy," he said before ribbing Sanders, whose personal net worth rose in recent years after his book became a best-seller. "As the only person on this stage who is not a millionaire or a billionaire, I know a thing or two about building a movement, because mayor of South Bend, Indiana, is not exactly an establishment fundraising powerhouse."

Buttigieg, since Iowa, has also struck a more aggressive tone when discussing Sanders.

Hoping to sow doubt in Democratic voters, he has suggested the Vermont senator would be a drag on downballot races and, echoing the angst of some of his supporters, questioned Sanders' ability to unify the party ahead of a November showdown with President Donald Trump.

"I respect Senator Sanders," Buttigieg said in Salem. "But in a moment like this, when the message goes out that you're either for a revolution or you must be for the status quo, most of us don't know where we fit, and would rather be part of a movement that makes room for all of us. This is a moment to come together."

It's a message Buttigieg re-upped in another fundraising email on Monday, when he blasted Sanders for pushing "the kind of my-way-or-the-highway politics that's polarized the country." Sanders, at an event in Manchester that morning, dug into Buttigieg again.

"Even in the newspapers today, you can see candidates conferring with their donors," Sanders said, before directly addressing his supporters. "You are my donors. We don't go to rich peoples' homes and get advice from millionaires and billionaires who are raising all kinds of money."

Reconciling the past

Pete Buttigieg and Sanders take a break during the Democratic presidential primary debate at Drake University on January 14, 2020 in Des Moines, Iowa.

Buttigieg put a different spin on Sanders' ideological commitment in his award-winning 2000 essay for the John F. Kennedy Profile in Courage Essay Contest.

"Fortunately for the political process, there remain a number of committed individuals who are steadfast enough in their beliefs to run for office to benefit their fellow Americans," Buttigieg wrote then. "Such people are willing to eschew political and personal comfort and convenience because they believe they can make a difference. One outstanding and inspiring example of such integrity is the country's only Independent Congressman, Vermont's Bernie Sanders."

Asked about those words during a 2017 interview on "The Axe Files," former top Obama strategist David Axelrod's podcast, Buttigieg praised Sanders for his "conviction politics," arguing they made him an effective messenger with independents and Republicans.

"I like to say, I'm like a hipster. I like to say that I knew about him before he was cool," Buttigieg said. "Not a lot of people were talking about Bernie Sanders (in 2000)."

Photos: Former presidential candidate Pete Buttigieg Photos: Former presidential candidate Pete Buttigieg Pete Buttigieg, the former mayor of South Bend, Indiana, poses for a portrait at his office in December 2018. Hide Caption 1 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg was an intelligence officer with the Navy Reserve from 2009 until 2017, and he served in the war in Afghanistan. Hide Caption 2 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg thanks supporters after he was elected mayor in 2011. Buttigieg was born and raised in South Bend and went on to attend Harvard College. He later became a Rhodes scholar. After a three-year stint at the consulting firm McKinsey and Company, Buttigieg came back to Indiana and lost a race for state treasurer in 2010. Hide Caption 3 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg listens to a question during a news conference announcing an interim police chief in March 2012. Hide Caption 4 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg paddles a raft during the East Race Waterway in July 2013. Hide Caption 5 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg delivers his State of the City address in February 2014. Hide Caption 6 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg is welcomed home in September 2014 after serving a seven-month tour of duty in Afghanistan. Hide Caption 7 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg speaks in November 2014 during a presentation ceremony for a newly redeveloped area in South Bend. Hide Caption 8 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg speaks out about the Religious Freedom Restoration Act that was signed in Indiana in March 2015. Buttigieg and other critics of the legislation, which was signed into law by then-Indiana Gov. Mike Pence, contended that individuals and businesses could use it to discriminate against the gay community on the basis of religion. Pence later signed an amendment that was intended to protect the rights of LGBT people. Hide Caption 9 of 28 Photos: Former presidential candidate Pete Buttigieg The State Theater in downtown South Bend shows its support for "Mayor Pete" after Buttigieg came out as gay in June 2015. Hide Caption 10 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg's name is Maltese and roughly translates to "lord of the poultry." His husband, Chasten, tweeted a list of possible pronunciations in 2018 that included "boot-edge-edge," "buddha-judge" and "boot-a-judge." Hide Caption 11 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg speaks at a debate-watching party in Chicago in September 2016. He was stumping for Democratic presidential candidate Hillary Clinton. Hide Caption 12 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg speaks during a Democratic National Committee forum in February 2017. Hide Caption 13 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg greets supporters during the DNC forum in February 2017. He was campaigning at the time to be the committee's chairman. Hide Caption 14 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg walks with Facebook CEO Mark Zuckerberg, a personal friend, who was visiting South Bend in April 2017. Hide Caption 15 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg appears on "Late Night with Seth Meyers" in June 2017. Hide Caption 16 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg kisses his husband, Chasten, after they were married in South Bend in June 2018. Hide Caption 17 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg announces in December 2018 that he would not be seeking a third term as mayor. Hide Caption 18 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg talks with a reporter in downtown South Bend in January 2019. Hide Caption 19 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg speaks to reporters in Washington after announcing his presidential ambitions. Hide Caption 20 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg speaks during the US Conference of Mayors in January 2019. Hide Caption 21 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg speaks during a campaign stop in Ankeny, Iowa, in February 2019. Hide Caption 22 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg signs copies of his book "Shortest Way Home" in February 2019. Hide Caption 23 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg speaks on stage during the South by Southwest Festival in Austin, Texas, in March 2019. Hide Caption 24 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg answers questions from supporters during a fundraising event in West Hollywood, California, in March 2019. Hide Caption 25 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg and former Vice President Joe Biden talk during a break in the first Democratic debates. Hide Caption 26 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg takes part in CNN's Democratic debates in July 2019. Hide Caption 27 of 28 Photos: Former presidential candidate Pete Buttigieg Buttigieg announces the end of his presidential campaign at an event in South Bend, Indiana, in March 2020. Hide Caption 28 of 28

A few years and one fiercely contested primary contest later, Buttigieg and Sanders are talking an awful lot about one another. Buttigieg was serenaded at a party dinner on Saturday night with chants of "Wall Street Pete" by the Vermont senator's supporters.

"Mayor Buttigieg was right in 2017," Sanders spokesman Mike Casca said of Buttigieg's interview with Axelrod. "Sen. Sanders has a record of bipartisan achievement that dates all the way back to his time as mayor of Burlington. He's always advocated for policy change from a place of conviction. Others? Not so much."

During a CNN town hall last week, Buttigieg was asked how reconciled the praise of Sanders in essay with their current clashes.

"What I really admired about Senator Sanders, and still do, is his consistency and willingness to say exactly what he believes," Buttigieg said. "It doesn't mean I agree with him. I didn't agree with him on everything then and don't agree with him on everything now."

Buttigieg under fire from both sides

Buttigieg speaks during the McIntyre-Shaheen 100 Club Dinner, Saturday, Feb. 8, 2020, in Manchester, New Hampshire.

For Buttigieg, the back-and-forth with Sanders is playing out like a Greek tragedy -- or comedy, depending on where you stand -- amid a less quirky pile-on from his moderate rivals, who have spent the last few days trying to blunt his momentum. In one of the primary's harshest ads, Biden mocked the former mayor as a small-time politician comically unqualified for the presidency.

The intra-moderate fighting put a smile on the face of Sanders senior adviser Jeff Weaver, who on Oscar night praised the editing of Biden's online ad, noting it was perfectly constructed to be clipped into short bites for consumption on cable news programs.

"Hats off for execution," Weaver deadpanned before Sanders took the stage in Keene on Sunday night, offering some cheeky praise to the Biden team.

The sudden focus on Buttigieg has caught even some Sanders supporters in New Hampshire -- and around the country -- by surprise.

Buttigieg said on Sunday he considered deficit reduction a priority, even though the issue is "not fashionable in progressive circles." The argument was hardly a new one; he's been making it for months. But when the comments were highlighted in a story that afternoon, the online left pounced, as if responding to a new development, and slammed the mayor for using -- in their view -- Republican talking points.

At the Sanders rally in Keene, a handful confessed to not having paid much mind to Buttigieg before last week. Others were complimentary, if ultimately wary of the young candidate.

"Buttigieg is very impressive, he just doesn't have experience," said Elizabeth Duffy, 57, who drove about an hour south with her husband to see Sanders in Keene. "What worries me (about Buttigieg) is he's been changing with the sort of demographic or consensus. Bernie doesn't do that; he sticks by what he believes in and I feel like Buttigieg is open to change in a way that I don't trust as much."

Though they aren't aiming their messages at the same voters, the depth of the primary field means that defections from Sanders' base -- even if they don't go to Buttigieg -- could help the former mayor on Tuesday night.

At a Buttigieg rally this weekend, also in Keene, Judy Lundahl and Christine Benson, two 71-year old New Hampshire residents, stood near the back of the room waiting for the candidate to speak.

Both of the women voted for Sanders in the last primary -- and both are planning to cast their ballots for someone else four years later.

"I don't want to diss Bernie," Benson said, "but the white men haven't done the best job."

Benson likes Buttigieg, but is likely going to back Warren on Tuesday. Lundahl is undecided between the two, whose support also overlapped in Iowa.

"I'm looking for somebody who's got some new ideas," said Lundahl, "who has some enthusiasm from the next generation that is going to hopefully solve some of the problems we have, that my generation and the generations before have created.

Lundahl said that she gave Sanders a shot this time around, but, after months of deliberation, decided to go elsewhere -- and threw away one of his 2016 campaign t-shirts to make it official.

"That was four years ago," she joked. "I put it in my rag bag."