Former New York City Mayor Michael Bloomberg officially entered the 2020 race Sunday, ending several weeks of will-he-or-won’t-he speculation about a late entry into the already-crowded Democratic primary.

Bloomberg’s entry was preceded by news of a massive television ad buy — $31 million, according to Advertising Analytics, which told NBC News it was the single largest single week expenditure the firm had ever tracked. A $30 million buy-in the final weeks of the 2012 race for then-President Barack Obama held the previous record.

The ad promotes Bloomberg's record as mayor and then promises "to rebuild the country and restore faith in the dream that defines us: where the wealthy will pay more in taxes and the middle class get their fair share; everyone without health insurance can get it and everyone who likes theirs, keep it; where jobs won't just help you get by but get ahead. And on all those things, Mike Bloomberg intends to make good."

It’s Bloomberg’s deep pockets and willingness to spend that could help him make up the difference of getting in several months after most of the already-established Democratic field. But his strategy to win is a risky one: skipping the early four nominating contests and instead of running what longtime Bloomberg aide Howard Wolfson called a "broad-based, national campaign."

He’ll also come up against a field stacked with strong competition, some with similar messaging to his own — like former Vice President Joe Biden, who has also hinged his candidacy on his ability to beat President Donald Trump next November — and progressive Senators Elizabeth Warren and Bernie Sanders, who are running on platforms of more structural change. And they’ve all been running for months, building organizing machinery as they go.

Still, Bloomberg Communications Director Jason Schecter said it’s not too late, citing polls that show Democratic voters have yet to firmly make up their minds on which candidates to support. Schecter said Bloomberg "has the skills to fix what is broken" and was motivated to run by concerns about "the possibility that we could lose next November" to Trump.

"We can’t afford another four years of this," he said.

Bloomberg declined to enter the race last March. At the time, sources close to him told NBC News that they didn’t see a path to victory with Biden in the race. But consternation from certain Democratic circles about the strength of the field — Biden has lagged while Warren surged throughout the summer and early fall — reignited talk of a Bloomberg run.

Perhaps the clearest signal that he had decided to run was Bloomberg’s recent disavowal of the stop-and-frisk policy he implemented as mayor and fiercely defended for years. Speaking at a black megachurch in Brooklyn, New York, last weekend, Bloomberg said: "I got something really important wrong … I want you to know that I realized back then, I was wrong — and I’m sorry."

A key South Carolina politician — Columbia Mayor Steve Benjamin — was in the crowd that day and told NBC News a few days later that he was "moved" by the humility in Bloomberg’s apology. He said he planned to endorse him if the former mayor decided to officially run.

Other 2020 hopefuls who have been running for months, however, have reacted forcefully against Bloomberg’s foray into the field, even before Sunday’s official announcement.

"I don’t think a person, just because they have billions of dollars, should sit back and say, 'you know what, yeah, I think I’ll run for election right now and drop $100 million,'" Sen. Cory Booker, D-N.J., told a crowd in Concord, New Hampshire, on Saturday.

Sen. Amy Klobuchar, D-Minn., also in New Hampshire on Saturday, said she doesn’t "believe you get the best candidate when there's such a bias in terms of money. I don't believe that's how this works."

Klobuchar, who has joked that she raised $17,000 from her ex-boyfriends during her first Senate run, joked Saturday of Bloomberg’s record ad buy: “Man, I’m not going to be able to make that up with the ex-boyfriends.”

Meanwhile, Warren — who hasn’t held back her feelings on billionaires, or Bloomberg — told said Saturday night “this election should not be for sale,” later adding that she doesn’t think the race “is going to be about TV ads versus TV ads” but instead about “grassroots movements.”