That money bought him an avalanche of TV ads, breathless media coverage, a humongous ground operation, dozens of endorsements and a nice surge in the polls.
And it let him claim a place in the top tier of Democratic candidates without any of the relentless work or scrutiny a presidential campaign usually demands.
The truth is, Bloomberg was screwing himself over. He built his campaign on quicksand.
Because on that debate stage, the scrutiny Bloomberg had managed to avoid for so long finally arrived, and no amount of money could save him from his own inadequacy.
It might sound like I'm shaming Bloomberg for being a multi-billionaire, or for self-funding his campaign. That's not the point here.
The point is the staggering arrogance of the man.
Bloomberg thought his wealth exempted him from the hard toil of campaigning. He disrespected the voters whose support he was trying to win.
You may have wondered why Australia's election campaigns take five weeks, while America's take more than a year. There's actually a very good reason for that length, as absurd as it seems – it gives voters as much time as possible to judge the full field of candidates.
Can they manage a national campaign? Can they win support from a diverse cross-section of the country? How well do they handle tough questions? Can they perform consistently in the spotlight? Do they have the stamina required for the job?
In a presidential system, which concentrates so much power around a single person, these questions matter even more than they do here.
The American voters might get it wrong sometimes, but they are always given more than enough information, because the process is designed to relentlessly test everyone who asks for their support.
Bloomberg decided he was above all that. He didn't need to be tested. He was obviously the correct choice.
He thought he could announce his candidacy months too late, skip the first part of the nominating process entirely, barely show his face in public, chuck some slick ads on TV and then swoop in as the Democratic Party's saviour.
Time to update Bloomberg's Wikipedia page...
Date of death: 2/19/2020 Place: Democratic Debate stage Cause: Elizabeth Ann Warren#DemDebate
Hours before this week's debate, Bloomberg's campaign had the gall to tell other moderate Democratic candidates to get out of the race and endorse him, claiming he was the only one capable of beating Bernie Sanders to the nomination.
"We are really down to a race where there are three people left who could really be considered viable to be sworn into office next year, and that's Bernie Sanders, Mike Bloomberg and Donald Trump," campaign staffer Dan Kanninen told reporters.
Bloomberg had yet to appear on a single ballot, but there he was, telling rivals with tens of thousands of votes to their names to make way for him.
We now see the result of that arrogance. Instead of the coronation he expected, Bloomberg delivered one of the most spectacular faceplants in American political history.
To borrow a sporting term, it was obvious within the first five minutes of the debate that he was not "match-fit".
Imagine what would happen if an AFL team skipped the entire regular season, then tried to jump straight into the finals series and compete. It would be rusty; a shambles; out of its depth; utterly unable to keep up with its more battle-hardened opponents.
Did Elizabeth Warren just end Bloomberg’s campaign? How many NDAs did Bloomberg force women to sign. She kept asking. He wouldn’t answer. Put a fork in him.
That was Bloomberg. When he took the stage in Nevada, surrounded by rivals who had been debating each other and sharpening their wits for months, he'd not debated anyone at all for more than a decade.
He had done no tough TV interviews during the campaign. No town halls with voters. Practically no actual campaigning. And it showed.
Compare him to Bernie Sanders, who has essentially been running for president non-stop since he lost the Democratic nomination to Hillary Clinton four years ago.
Compare him to Pete Buttigieg, the no-name former mayor of a mid-sized city, who started his campaign with no personal fortune, no donors and no one even knowing who he was.
Buttigieg was only on the stage this week because of months of ceaseless effort – meeting voters, listening to their concerns, refining his message, earning donations, going on any show that would have him, and performing at a consistently high level.
Bloomberg had none of that experience under his belt. Why bother doing the work and earning your spot when you can just buy it?
"Remember, I only entered into this race 10 weeks ago. All of my associates here have been at this for a couple of years," Bloomberg said at one point, scoffing at the idea that he should be ready to release his tax returns.
"That's right, we have. Engaging with voters and humbling ourselves to the backyards and diners," Buttigieg shot back at him.
It was a tiny moment, easy to miss, but Bloomberg's lack of self-awareness was telling.
The more explosive moments exposed him as well.
Time after time, Bloomberg faced entirely predictable questions about his record, both as mayor of New York and as a businessman. Every time, he flubbed the answer.
Elizabeth Warren was his chief tormentor. She repeatedly grilled Bloomberg on his history of sexist comments and alleged sexual harassment of female employees.
Warren's dismantling of Bloomberg over his treatment of women was one of the most precise and devastating political attacks I have witnessed in twenty years of following this stuff
"I'd like to talk about who we're running against. A billionaire who calls women 'fat broads' and 'horse-faced lesbians'. And no, I'm not talking about Donald Trump. I'm talking about Mayor Bloomberg," she said.
That was her very first line of the night, and it set the tone perfectly.
Asked about the harassment allegations a few minutes later, Bloomberg responded bizarrely, reeling off a list of women he had employed in prominent positions.
"I hope you heard what his defence was. 'I've been nice to some women,'" Warren interjected.
She brought up the unknown number of nondisclosure agreements women had signed with Bloomberg's company over the years.
"Mr Mayor, are you willing to release all those women from those nondisclosure agreements so we can hear their side of the story?" Warren asked.
Bloomberg refused. He babbled about most of the women in question "maybe not liking a joke" he'd told, and drew audible groans from the crowd when he insisted all the nondisclosure agreements were "consensual".
She asked how many agreements there were. He wouldn't say.
The whole exchange was brutal.
I'm not suggesting Ms Warren's attacks were easy to repel. There are heaps of problems with Bloomberg's record that would trouble even the cleverest political consultants.
But if he had bothered to campaign properly before this week – to subject himself to the same process as everyone else on stage – he would not have been forced to confront those problems for the first time with an audience of 20 million people watching.
Bloomberg could have spent months refining his answers and easing voters' concerns. Instead he expected those voters to support him, and his rivals to get out of the way, before he had been tested even once.
Any other candidate's campaign would probably be over after such an inept performance.
The thing is, I remember saying the exact same thing about Donald Trump's incoherent word salads in the Republican debates four years ago. Look what happened to him.
And Bloomberg has an advantage even Trump lacked – if things get really bad, he can always write himself another $400 million cheque.