Raleigh, North Carolina (CNN) Pete Buttigieg had a plan heading into February: Turn a strong performance in Iowa into enough momentum to compete in New Hampshire , notch a strong showing in Nevada and survive South Carolina .

By winning the most delegates in Iowa and placing within a few percentage points behind Vermont Sen. Bernie Sanders in New Hampshire, the former South Bend, Indiana, mayor successfully implemented the first two steps of that plan. But he also placed a distant third in Nevada and got trounced in South Carolina, finishes that highlighted the former South Bend, Indiana, mayor's persistent issues with voters of color.

And on Sunday, Buttigieg exited the presidential race, ending an unlikely campaign that vaulted the once-unknown mayor to a top presidential contender.

The decision to exit the race is a reflection that Buttigieg's path toward the nomination was far narrower headed into March than just one month ago. That reality forced the candidate on Sunday to confront the real possibility that, without a significant change in the state of the race, his campaign would have to end.

Buttigieg conferred with advisers on Saturday night about his path forward. But he also told supporters in Raleigh, North Carolina, that he is "proud of the votes we have earned, and I am determined to earn every vote on the road ahead."

The mayor then spoke with aides again on Sunday and opted to end his run. He will hold a call with all of his staff to discuss his decision to drop out, two aides tell CNN.

His uncertain path ahead was even clear earlier in the day when he met with Jimmy Carter in Plains, Georgia, on Sunday. After the former president lauded Buttigieg, he remarked: "He doesn't know what he's going to do after South Carolina."

The problems for Buttigieg were particularly acute after South Carolina. The former mayor had long dealt with pressure from the left and Sanders, but former Vice President Joe Biden's rise also put pressure on him from the party's center, where scores of the donors that had long backed Buttigieg were eying Biden as a more viable option.

The challenges for Buttigieg's strategy rest on three unexpected realities: A severely delayed result out of Iowa, Sen. Amy Klobuchar 's boost in New Hampshire and former New York Mayor Michael Bloomberg 's more forceful presence in the race ahead of the Nevada caucuses.

"There's still a lot of oxygen being sucked up in the race," said Mike Schmuhl, Buttigieg's campaign manager, said before the former mayor got out. "When you stack all those people (running) up, there's not a lot of space or not a lot of wiggle room for any campaign to operate. And so, we're kind of in a crunch right now between South Carolina and Super Tuesday."

Buttigieg aides argued for months that the former mayor, by showing he could win in Iowa, would be able to convince skeptical voters across the country that he was a safe bet and his poll numbers in South Carolina and nationally would begin to surge in the back half of the month. Many aides likened it to what happened to Barack Obama in 2008, where a win in Iowa catapulted him to not only electoral success, but a surge of money.

That didn't happen. Buttigieg finished far behind Biden in South Carolina, national polls have found him hovering in the high single digits for months and his campaign is lowering expectations heading into Super Tuesday.

"The path has tightened and is tightening for everyone,"a top Buttigieg aide said before the former mayor decided to end ended his bid. "That is definitively true, but don't think that is unique to our campaign."

The aide continued: Buttigieg "knows where we are. He has been aware of this for a long time."

After delivering his concession speech on Sunday, Buttigieg spoke to Biden by phone, two people familiar with the conversation say.

Biden congratulated Buttigieg on his campaign and asked for his endorsement. Buttigieg did not make an immediate decision, telling advisers after the call that he wanted to think about it overnight. An endorsement for Biden is likely, two people close to Buttigieg say, but whether he makes the decision before Super Tuesday is unclear.

The Iowa swagger is gone

Buttigieg speaks at a Meet the Candidate campaign event January 31, 2020, in Sioux City, Iowa.

The uncertain state of Buttigieg's campaign was clear in the final days before the South Carolina primary, where the candidate spent the week trying to do something he has been unable to do for the better part of a year: Establish a reliable foothold with black voters.

With a distant fourth-place finish, he wasn't able to do that.

The competitiveness with which the Buttigieg campaign approached Iowa, where the mayor barnstormed the state by often headlining five public events in a single day, was long gone in the days leading up to the South Carolina primary. Instead, Buttigieg spent his days headlining at most three events, with some being invite-only roundtables where the audience was, exclusively, the media.

The former mayor's campaign had already begun lowering expectations heading into Super Tuesday, telling reporters that its focus was on strategically deploying resources across the country and hoping to rack up delegates by at least meeting the delegate threshold -- 15% -- in key congressional districts.

"Our goal is to minimize Sanders' margins on Super Tuesday and rack up delegates in the March 10th and March 17th contests, which are much more favorable to us," the campaign wrote in a memo that was used as a fundraising pitch on February 25.

But Buttigieg realized, according to aides, that even with a surgical focus on delegates, he did not have the momentum needed to compete nationally.

Buttigieg's campaign was also not as flush with campaign cash as it was months ago.

Money was still consistently coming into the campaign, said a source with knowledge of the campaign's fundraising, with the campaign raising above its daily average over the last few days. But the campaign's federal election reports have shown Buttigieg's operation is quickly spending whatever money it brings in -- and then some.

According to his financial filing for January, the former mayor entered February with $6.6 million in the bank and spent 227% more than they raised the first month of 2020. And the campaign has yet to hit their goal of raising $13 million before Super Tuesday.

One reason for the issue: The percentage of Buttigieg's fundraising from small dollar donors -- over time -- has fallen from 65% in early 2019 to just 29% in January, according to his financial filings.

Those money problems led the campaign to only reserve $1.6 million in television ads in Super Tuesday states, according to data from CMAG, a small number that pales in comparison to most of his competitors. And because they were eager to avoid spending TV advertising money in expensive markets, the former mayor had trips planned to Raleigh, North Carolina; Dallas and Oklahoma City in the days before Super Tuesday as a way to get earned media without spending money on television ads.

How Buttigieg got here

Buttigieg aides believe there is plenty of blame to go around for the campaign's demise.

The former mayor's month started better than most would have expected with a strong showing in Iowa.

But the Iowa results, because of the chaos that befell the state on caucus night, were not officially certified until weeks after Iowa Democrats caucused on February 3. Because the state party was ill-prepared for the caucus and used a faulty app that significantly delayed the reporting of results, much of Buttigieg's momentum out of the state was blunted and, while money followed the win, it wasn't as substantial as top campaign aides expected.

"I would say that there is a little frustration that there wasn't more clarity on caucus night in Iowa," said Schmuhl, "because I think that that could have been potentially much bigger for us and really helped our catapult strategy that we have devised a long, long time ago."

The delay, in the eyes of Schmuhl and others, thwarted their plan to try to mimic Obama's success in 2008.

Reggie Love, a former top aide Obama aide who is now backing Buttigieg, said, like his former boss, "Iowa did validate Pete."

But even Love admitted it hasn't been as clear for Buttigieg.

"I think it proved that his message does resonate with the toughest voters in the country," he said. "But Bernie also did well and there was a lot of noise around the process and by the time you had clarity around what even actually was validated, you were four days or three days to the New Hampshire primary."

Buttigieg then came within a few percentage points of Sanders in New Hampshire and picked up more national delegates from the state with a second-place finish.

But that performance was overshadowed by a resurgent Klobuchar, who used a strong debate days before the state voted to finish third in the primary. Klobuchar, not Buttigieg, saw her media attention surge and the Minnesota senator raised more than $12 million in nine days in the middle of February, a boom in money for her cash-strapped campaign.

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

Klobuchar's rise corresponded with the rise of former New York Mayor Mike Bloomberg, whose poll numbers surged in early February to the point that he qualified for the Democratic primary debate in Las Vegas on February 19. Bloomberg's ascension -- combined with his spending of more than $500 million on ads just to propel his run -- sucked up considerable media attention and further divided the growing anti-Sanders electorate.

Buttigieg responded to this one-two-punch of momentum killers by looking to focus voters on the reality of both his and the party's situation.

"We've got to wake up as a party," Buttigieg said during a February debate in Las Vegas. "We could wake up two weeks from today, the day after Super Tuesday, and the only candidates left standing will be Bernie Sanders and Mike Bloomberg, the two most polarizing figures on this stage."

The message continued throughout the former mayor's run in Nevada, where Buttigieg finished a distant third behind Sanders and Biden.

Buttigieg responded by turning up the heat on the Vermont senator, stoking some of the fears that Democrats have long held about what Sanders, as nominee, would mean to down ballot races. And his campaign put a finer point on it in the days leading up to the first in the west caucus.

"If the dynamics of the race did not dramatically change," the campaign wrote in a memo, "Democrats could end up coming out of Super Tuesday with Bernie Sanders holding a seemingly insurmountable delegate lead."

The question for Buttigieg's campaign going forward was whether they could recover from their February strategy failing to deliver the momentum they had anticipated.

And Buttigieg, in a possible sign that he saw himself at the end of his unexpected rise, even slipped at his CNN town hall and said he was at the "end" of his campaign.

"Somebody once called (running for President) an MRI of the soul," he said. "By the end of it -- or, frankly, by the middle of it, you feel like people have gotten to know just about everything about you."

This story has been updated to reflect that Buttigieg will end his campaign on Sunday.