Jeb Bush: Inside the Demise of the One-Time Frontrunner's Campaign

— COLUMBIA, South Carolina -- On a sweltering day in Miami last June, surrounded by a diverse group of supporters, Jeb Bush announced his candidacy for president of the United States.

"My message will be an optimistic one," Bush promised. "I will campaign as I would serve: Going everywhere, speaking to everyone, keeping my word, facing the issues without flinching and staying true to what I believe."

In a remarkable turn of events, eight months later, Bush -- the son and brother of presidents -- suspended his campaign, flanked by his tearful wife and youngest son.

But in a race for the Republican nomination marked by tumult and change, one thing had not: His message.

"I committed that I would campaign as I would serve," Bush said, repeating almost word for word a line from that very first speech. "Going everywhere, speaking to everyone, keeping my word, facing the issues without flinching and staying true to what I believe."

Bush, the former two-term governor of Florida, famously said in December 2014 that Republicans might have to be willing to "lose the primary to win the general without violating your principles."

He seemed to do just that.

In countless town hall meetings, conversations with voters and interviews with the media, Bush defended policies, some of which were anathema to the Republican Party. He favors a path to legal status for undocumented immigrants and supports the Common Core education standards. His wife is Mexican-born and he speaks fluent Spanish. He seemed to be the candidate the party needed; one who could woo moderates and Hispanic voters, a voting bloc the party desperately needed.

But by the time he reached South Carolina, it wasn’t policy that doomed the man who entered the race as the presumptive nominee, it was personality: The outsize presence of Donald Trump, a rival so fiery, so divisive, so emblematic of the anger of the GOP base that Bush probably never imagined could have stopped him -- the heir to one of America’s most powerful political dynasties -- dead in his tracks.

Here’s a look at how it all happened:

'Low-Energy': The Blow That Began It All

Four days after Bush formally entered the presidential race, a NBC News/Marist/Wall Street Journal poll showed him sitting atop the pack. But on Aug. 19, as Bush and Trump held dueling town halls in New Hampshire, the New York businessman uttered this phrase: "Jeb Bush is a low-energy person."

Bush never led in the polls again.

It is hard to overstate how fatal a blow this proved to be. Bush and his advisers, long under the impression that Trump’s campaign would fizzle, ignored the former reality TV star and his constant flurry of insults.

"I think it was every campaign and the media that thought Trump wouldn’t make it through the fall," one senior adviser told ABC News.

By the time campaign advisers realized how effective the simple attack had been, it was probably already too late. Bush began vehemently attacking Trump, calling him "unhinged" after his proposal to ban Muslims and often attacking him on the stump for his disparagement of women, Latinos, and prisoners of war.

The two rivals sparred in debates, Bush becoming better along the way, some critics even saying he won his and Trump's most recent exchange at the debate in Greenville, South Carolina, last weekend.

But while Bush played tough, his super PAC didn't play along.

How Shock and Awe Went Down the Drain

That super PAC, Right to Rise, started out with a massive war chest of more than $100 million. At its helm, was Mike Murphy, the revered political consultant. But the super PAC also underestimated Trump's reach, spending the majority of its cash flooding the airwaves going after other candidates in the race.

A ProPublica study found that of the $85 million the group spent on advertising, only $25,000 was directed solely at Trump; the apparent aim was to clear out the rest of the pack, especially Bush's former protege, Florida Sen. Marco Rubio.

New Hampshire was where Right to Rise really bet the ranch. Between it and Bush's own campaign, their spending accounts for 41 percent of all Republican spending in the state, spending 10 times more than Donald Trump.

Despite their efforts, Bush came in fourth.

Right to Rise released its spending reports the day of the South Carolina primary; it raised only $369,000 in the month of January. It was taking in $551,000 per day during the first half of 2015, spending money with an astounding 9,349 percent burn rate.

The money simply didn’t matter.

The Endorsement That Ended It All

South Carolina Gov. Nikki Haley is a rising star in the Republican Party for whom Bush had campaigned. Her endorsement was so coveted that the candidate not only sent top adviser Sally Bradshaw to make the pitch, he also deployed his brother, the former president, to personally court her.

But just days before the primary, she threw her support behind Rubio.

It was a major blow. A Winthrop University poll conducted in December of 2015 showed Haley had an 81 percent approval rating among likely Republican primary voters. Bush had long espoused the need for a governor as president. To have Haley, who referred to him as a "dear friend," endorse a rival whom Bush was painting as inexperienced was crushing.

"She’s a great person," Bush said of the snub. "I'm disappointed she didn't endorse me."

When asked about the impact of the governor endorsing the young senator, Bush told ABC News, "I don't know. We'll see on Saturday."

Barbara's Boy

As he reached the end, Bush had brought in the cavalry. His brother, still popular among Republicans, campaigned with him at a joint rally and was featured in several ads. His mother slowly trudged through snow in New Hampshire and wooed the crowd in South Carolina -- always in tow, her walker, adorned with the "Jeb!" logo.

Bush had not mentioned his family with great regularity until late in his campaign; the idea of a third Bush in office was repugnant to some.

"The legacy of the Bush family, even though I voted for the Bushes, I get tired of seeing a political family in leadership positions and I think we need diversity," said Jim Bartal, of Anderson, South Carolina.

For others, Bush's candidacy was the anti-Trump, a restoration of a civility in politics. Laurie Urquhart, of Hollis, New Hampshire, was in the audience when the former first lady first campaigned for her son.

"I think for the primary she's fostering that love for people who like Bush/Reagan, that whole era, reminding them of what they liked," she said.

During the final town hall of Bush's campaign, his mother introduced him to the crowd in Central, South Carolina.

"They say these other men are smart. They’re smart but they haven’t got the background that Jeb has," she said. "He's done the most amazing things as governor. ... He's a great husband. He's a great friend. He's loyal ... my boy, Jeb."

The Bush family brings with it certain values. You don't engage in alley fights, you always show up on time, you don't brag, lest, as Bush says, you encounter the backhand of Barbara Bush.

The Bully vs. the Technocrat

Bush had to learn how to fight, to take on Trump -- a talent that did not come easily.

"In debate prep, you learn to have to have the last word," he told a Leesville crowd last week. "Because he's [Trump] a bully. You just have to keep talking through it. It's not a skill I thought necessary."

What he thought necessary was what he focused on: An undying attentiveness to policy and detail. He was accessible and respectful of the press and, much to the chagrin of his communications team, unable to refuse a question he was asked.

But in the end it seems he was a candidate not for this time, whose sensibility was no match the latent anger of the Republican electorate of 2016, whose policies and genteel upbringing could not withstand the fiery rhetoric that so captured this race.

As he left the stage Saturday night for the final time as a candidate, his eyes grew misty.

"I firmly believe the American people must entrust this office to someone who understands that whoever holds it is a servant, not the master, someone who will commit to that service with honor and decency," he said.

With those few words, an era in American political history had ended.

ABC News’ Ryan Struyk contributed to this report.