Joe Lockhart was White House press secretary from 1998-2000 in President Bill Clinton's administration. He co-hosts the podcast "Words Matter." The opinions expressed in this commentary are his own. View more opinion at CNN.

(CNN) Michael Bloomberg has wanted to be President of the United States for a long time. He toyed with the idea both in 2008 and 2016. But as a shrewd data-driven political leader, Bloomberg must have had a difficult time seeing a path to winning the Democratic nomination. That is, until now.

With the lackluster performance of the original frontrunner, former Vice President Joe Biden, and the Democratic establishment's unease with Sen. Bernie Sanders, Bloomberg jumped into the lane opening up in the 2020 race, focusing on the Super Tuesday primaries in March.

But I suspect the most compelling reason Bloomberg made his decision to jump in was not the rest of the Democratic field, but one person who defines American politics today -- President Donald J. Trump. And, more to the point, Democrats' obsession with defeating him in the fall.

Bloomberg is an unlikely Democratic nominee. A onetime Republican, the billionaire former mayor of New York hardly appeals to the classic Democratic coalition. His support of the New York Police Department's "stop and frisk" policy disproportionally impacted minority communities and earned him the antipathy of black leaders both in New York and around the country. His public and private comments on race and policing have made him unelectable among many Democratic voters.

His wealth and Wall Street background also alienates many of the core supporters of Bernie Sanders and Elizabeth Warren. His comments on income inequality, which were attacked this week by Warren, run counter to several key Democratic messages. And his massive wealth and willingness to spend unlimited amounts run against the party's instinct to limit the amount of money in politics.

While a contemporary of Joe Biden, he's not spent the last 40 years building relationships and support among rank and file Democrats, including union leaders, DC insiders and the foreign policy establishment. Finally, he's not a great speaker and qualifies as a charter member of the charisma-challenged caucus.

So, why are Democrats considering overlooking Bloomberg's baggage now to the point that he's currently running as high as third, according to a Quinnipiac poll ? Because in my view, rank and file Democrats are so invested in the imperative to defeat Donald Trump they may well be willing to ignore the issues that likely kept Bloomberg out of the race at the outset. Earlier this week, a resurfaced recording from 2015 revealed Bloomberg defending stop-and-frisk, as well as racist policing in New York City.

Now, it's not all baggage with Bloomberg. He's spent massive amounts of his personal wealth funding gun safety campaigns around the country. With that, he's built a network of political supporters who've benefited from his financial support. His leadership and financing of climate change initiatives has also provided him with a base of liberal and young leaders around the country.

But as in many puzzles, the answer is following the money. And that's what Bloomberg has, and lots of it. And unlike some other billionaires, he's willing to spend it, as much as it takes, to win both the nomination and the presidency. He's already spent more than $300 million on advertising alone and has built a nationwide campaign staff of almost 2,500 people.

He's also proved he can get under President Trump's skin with comments like his response when asked what a race between two billionaires would be like. Bloomberg deadpanned: "Who's the other billionaire?" That, and ads that scorch the President's character and record, have served as a salve for Democrats near hysteria that Trump may be reelected for a second term.

Many donors are privately excited by Bloomberg for selfish reasons -- they won't have to pony up big sums in both the primaries and general election to help him get elected. He will self-fund the campaign completely.

Other Democrats were pleased he made the commitment to spend into the billions through the fall even if he's not nominated. And party professionals are tickled that Bloomberg is spending massive sums attacking Trump in battleground states right now when Democratic candidates can't afford it.

Finally, the massive alarm sounded by political professionals about the online dominance of the Trump campaign has literally been wiped out overnight by Bloomberg's spending on social media platforms

There are still obstacles ahead. Bloomberg has not participated in a single debate and has until this week largely avoided the scrutiny of the media and the other candidates. He's needed to prove he's more than an advertisement candidate, and can both deliver a punch on the stump and take one himself.

Advertising professionals can make anyone seem exciting and compelling; the normally staid Bloomberg will have to prove he's got some persuasive powers beyond the largesse of his checkbook.

Get our free weekly newsletter Sign up for CNN Opinion's new newsletter. Join us on Twitter and Facebook

The single-minded mission among Democrats partially explains why Joe Biden stayed on top of the Democratic field for so long. Now that he's faltered in two straight contests , Democrats increasingly are looking to Bloomberg as the solution to the problem they care about above all else—defeating Donald Trump. And they might be willing to give the previously thought "unelectable" Mike Bloomberg a long look for the Democratic nomination for President.

What was very unlikely in 2008 and 2016, is now looking like a real possibility. And Bloomberg is willing to see just how far a political candidate can get on a couple of billion dollars. And Democratic voters look willing to consider an unlikely candidate because he can do the thing that matters most to them. Win.