(CNN) Joe Biden's scramble to regain his footing in New Hampshire after a poor showing in Iowa ended in a half-filled Radisson Hotel ballroom.

Biden wasn't there.

Instead, the former vice president appeared by video conference from South Carolina to briefly thank the die-hard New Hampshire supporters who had come. He was in fifth place in the Granite State by the time he spoke, mired in the single digits and falling short of the threshold needed to collect delegates -- a dramatic descent for a candidate who had been the front-runner for much of 2019.

Victory now seems elusive for a two-term vice president who has premised his entire campaign on his ability to beat President Donald Trump , only to see that electability argument undercut by crushing losses in the first two Democratic contests. He's in the worst position after the first two contests of any sitting or former vice president in history: His modern predecessors who attempted bids at the White House either won in New Hampshire (Al Gore, George H.W. Bush and Richard Nixon) or placed second (Walter Mondale) and went on to win the nomination.

Biden is now also facing a looming challenge in Super Tuesday and beyond in the candidacy of former New York Mayor Michael Bloomberg , who appears to be cutting into his support with African American voters and has spent more than $300 million introducing himself. Biden's advisers insist that Bloomberg has not yet been vetted.

"He is not tested," Biden campaign Chairman Cedric Richmond, a Louisiana congressman, said of Bloomberg Wednesday.

Supporters of Democratic presidential candidate former Vice President Joe Biden watch as Biden, behind right, and his wife Jill Biden, behind left, appear in a video transmission during a primary election night rally.

And in a call with reporters Wednesday, campaign advisers argued that no one should overlook Biden's durability as a candidate, despite his losses in Iowa and New Hampshire.

"This thing isn't over," senior Biden adviser Symone Sanders said Wednesday. "Don't count us out. "

But Biden's collapse in Iowa and New Hampshire was rooted in self-inflicted problems. His message was muddled. He mumbled through some of his lower-energy campaign events -- leading some voters to wonder what had happened to the dynamic vice-presidential candidate they saw in 2008 and 2012. His events continually lacked the electricity that Democrats expected from a front-runner.

"If he wants to keep people, he's got to instill confidence somehow, and that's not working at the moment," one source close to the campaign said, warning of the challenge that Biden faces from Bloomberg. "I think Biden people are loyal enough that they'll stick with him, but that said, there's also going to be people looking for off-ramps."

"There's a lot riding in the next two weeks for him but he's also got to prove it. I love him, but he's got to prove it," the source added.

With his national poll numbers falling, his support among black voters in question, his campaign is scrambling to show that it is fixing problems within its organization -- elevating Barack Obama campaign veteran Anita Dunn , for example, to have final decision-making authority over campaign manager Greg Schultz.

But Biden's frankness about his campaign's weaknesses has sometimes cast a shadow over efforts to reboot. He arrived in New Hampshire promising he'd recover from the "gut punch" of results from Iowa. Within days, he was publicly forecasting his own failure in the Granite State at a nationally televised debate.

"I took a hit in Iowa and I'll probably take a hit here," Biden said at the debate. "Traditionally, Bernie won by 20 points last time. And usually it's the neighboring senators that do well."

On Tuesday night, he told his crowd in South Carolina that they'd heard the verdicts of only "the first two of 50 states."

"Where I come from that's the opening bell, not the closing bell," Biden said.

But increasingly, Democratic voters are wondering whether it should be his fight.

Warning signs in Iowa

The day after he arrived in New Hampshire, Biden finally said aloud what virtually everyone in the Democratic Party has been saying privately.

"We took a gut punch in Iowa," the former vice president told New Hampshire voters who had gathered in Somersworth last Wednesday. "But look, this isn't the first time in my life I've been knocked down. ... None of you have been handed everything just on a silver platter."

But it was Biden's silver platter advantages when he entered the race last April that made his weak finish in Iowa so stunning. None of his rivals had the connections developed from serving two terms in the White House. None of them entered with his deep, big-donor list.

The fiasco that engulfed the Iowa Democratic Party last week masked that fact that Biden won very few counties in a state that had launched the man who chose him as his vice president in 2008.

Within his campaign before the caucuses, there was a profound sense of nervousness.

One major warning sign had come three months earlier, at the November Liberty and Justice Celebration in Des Moines, when the enthusiasm gap between Biden and other candidates became most apparent.

Biden walks on stage to speak at the Iowa Democratic Party's Liberty and Justice Celebration, November 2019, in Des Moines, Iowa.

Massachusetts Sen. Elizabeth Warren's section was a sea of volunteers in green T-shirts (even some of her empty seats were draped with her campaign colors).

Then-South Bend, Indiana, Mayor Pete Buttigieg 's team, in yellow, bought every ticket that his campaign was permitted to buy -- and they were clearly energized, showing representation from all of Iowa's 99 counties.

In Biden's section, however, there were notable gaps of empty seats and boxes of untouched blue thundersticks on the floor. It was a failure of organization that upset the candidate and was a wake-up call for his campaign.

Shortly after that event, Biden angrily told his campaign chairman, Steve Ricchetti, that things had to change. The campaign responded by stepping up his presence in Iowa and dispatching the deputy campaign manager, Pete Kavanaugh, to the state to oversee the organization.

Durability amid early stumbles

Biden survived several major missteps in 2019. The first was in June, when he created confusion by telling a woman on a rope line that he had changed his position on the Hyde Amendment , which bars federal funds from being used for most abortions. When the clip caught fire on social media, his campaign said he had not altered his stance.

That created a new source of blowback -- one that could have crippled his support among female voters. Ultimately, amid the backlash, Biden said he was dropping his support for the Hyde Amendment.

Biden then survived an attack by California's Sen. Kamala Harris during the June debate, when she challenged his opposition to the federally mandated busing of schoolchildren to diversify schools decades ago in neighborhoods that opposed it. He also faced criticism for having touted his ability as a young senator to work with segregationists, which he cited as an example of his skill in forging compromise.

The hopefuls who attacked him mostly vociferously in debates -- Harris, Rep. Eric Swalwell of California (who told Biden it was time to pass the torch) and Julian Castro, a former housing and urban development secretary (who suggested Biden was losing his memory), have all dropped out of the race.

The campaign faced a new series of challenges last summer, when the White House whistleblower flagged Trump's obsession with digging up dirt on the Bidens, namely Biden's son Hunter, who served on the board of a Ukrainian energy company while Biden was vice president.

Trump and his allies have repeatedly made unfounded and false claims to allege that the Bidens acted corruptly in Ukraine. Trump's efforts to damage Biden and his family later became a central part of the Democrats' impeachment case against the President, who was acquitted by the US Senate last week.

Some of Biden's worst days on the trail came when he was questioned about Hunter, who he often referred to as his only surviving son -- a reference to the loss of 46-year-old Beau Biden in 2015 to brain cancer.

Biden became visibly angry at an event in early December in Hampton, Iowa, when a retired farmer alluded to Hunter's position on the energy company board in Ukraine and accused the former vice president of "selling access to the President."

The voter accused Biden of sending his "son over there, to get a job and work for a gas company" with "no experience with gas, nothing."

"You're a damn liar, man, that's not true," Biden replied, challenging his antagonist to a push-up contest when the man told him he was "too old" to run for president.

Over time, Biden became less rattled by those kinds of encounters. At a recent event in Nevada, protesters stood up, each one holding a letter to spell: "Where's Hunter?" Biden calmly replied that his son was doing fine.

A chaotic week in New Hampshire

After losing to Vermont's Sen. Bernie Sanders , Buttigieg and Warren in Iowa -- with Minnesota's Sen. Amy Klobuchar finishing on his heels -- Biden landed in New Hampshire ready to get aggressive.

In Somersworth, he attacked by Sanders and Buttigieg by name.

"If Senator Sanders is the nominee for the party, every Democrat in America up and down the ballot, in blue states, red states, purple states, in easy districts and competitive ones, every Democrat will have to carry the label Senator Sanders has chosen for himself," Biden said. "He calls himself a democratic socialist. Well, we're already seeing what Donald Trump is gonna do with that."

Biden clenches his fist as he speaks at a campaign event, February 5, in Somersworth, New Hampshire.

The former vice president also told voters they would be taking a risk by nominating the 38-year-old Buttigieg: "I do believe it's a risk, to be just straight up with you, for this party to nominate someone who's never held an office higher than mayor of a town of 100,000 people in Indiana."

But on Wednesday night, Biden made a confounding move: He left the state, flying home to Delaware to prep for the Democratic debate two nights later.

He was off the trail Thursday, and only returned Friday for the debate -- an absence that was glaring as several of his rivals kept up busy schedules.

Biden turned in a feisty debate performance on Friday night, and cranked the attack on Buttigieg up to a new level Saturday morning, when his campaign released the most negative advertisement of the election cycle to date -- 98 seconds of mocking and belittling Buttigieg's accomplishments as mayor in a spot that appeared on Facebook and YouTube.

"We're electing a president," the narrator says. "What you've done matters."

Later that day, after a campaign stop in Manchester, Biden -- who handlers had largely kept away from the press for months -- held a news conference that turned into more of a vent session aimed at his rivals.

"Oh, come on, man," Biden told reporters of Buttigieg. "This guy's not a Barack Obama."

Saturday night in Manchester, Biden's organization would be tested again -- and show more signs of weakness.

The McIntyre-Shaheen dinner was an event much like Iowa's Liberty and Justice Celebration, attended by thousands of activists and supporters of the candidates.

Buttigieg, Warren, Sanders and former Massachusetts Gov. Deval Patrick all brought massive, raucous cheering sections. So did Klobuchar, whose section wrapped around a corner of the Southern New Hampshire University arena seats and spilled onto the floor.

Biden had a corner. It was more organized than Iowa, with all of his supporters sitting close together. But it was much smaller than his rivals' sections.

Biden speaks during the McIntyre-Shaheen 100 Club Dinner, February 8 in Manchester, New Hampshire.

The McIntyre-Shaheen dinner brought a sudden shift in Biden's message, too.

Gone were the attacks on Buttigieg and Sanders. Instead, he focused on connecting his own life experiences and sense of morality with his political achievements -- underscoring why he'd fought so hard to enact the Violence Against Women Act and praising the motives of his Democratic rivals.

"I'll be damned if I'm going to stand by and lose this election to this man," he said of Trump.

But on Monday morning, Biden focused on Trump's visit to New Hampshire, pre-butting the President on the economy -- starting his day in Gilford with a backward-looking speech saying that former President Barack Obama's administration deserved the credit, rather than Trump.

"Trump talks about the longest job growth in American history. One hundred and twelve months of increased employment and growth. Trump has only been president for 35 of those months. But guess where he got that good economy from? Obama-Biden administration," Biden said.

The swerving messages -- from attacks to morality to the economy in a three-day stretch -- gave the appearance of a candidate who was desperate to find something that worked for him.

This time, though, Sanders and Buttigieg had already proved their strength in Iowa. And Klobuchar was surging on the strength of Friday's strong debate performance.

"I thought I had my mind made up 100% for Biden, but then in the debate the other night I was really impressed with Amy Klobuchar. So now I'm not sure," said Peg Landry, a 60-year-old software consultant from Salem.

"I've been leaning toward Biden. But I haven't really been impressed with Joe in the debates, so I want to see him in person," said Valerie Brown, a 64-year-old health care consultant from Derry, who saw Biden campaign in Hudson.

Of his debate performance, she said: "Sometimes he can get caught up in his own language and he can kind of lose his train of thought. And just, not the energy. He just seems a little -- he seems a little old."

By Tuesday morning, Biden had decided to forgo his election-night party in New Hampshire in favor of a launch party with Richmond in South Carolina, his "firewall" state because black voters there make up a majority of the Democratic electorate.

Biden warned the South Carolina crowd on Tuesday night about the lack of minority support for two of his key rivals, Buttigieg and Klobuchar.

"Up until now, we haven't heard from the most committed constituency in the Democratic Party -- the African American community -- and the fastest growing segment of society, the Latino community," Biden continued. "99.9% -- that's the percentage of African American voters who have not yet had a chance to vote in America."