Former New York City mayor and billionaire businessman Michael Bloomberg filed federal papers on Thursday officially declaring himself a candidate in the crowded 2020 Democratic presidential field, just weeks before the first primary contests.

Bloomberg's team said that while he still had not made a final decision about whether to run, filing the paperwork was necessary to comply with election law after Bloomberg had registered for several state ballots. The filing allows him to begin raising and spending money on a campaign in accordance with election law.

Federal Election Commission rules state that an individual running for president "becomes a candidate when he or she raises or spends more than $5,000 in contributions or expenditures." Although the FEC allows a grace period "to test the waters," that changes once an "individual decides to run for federal office or conducts activities that indicate he or she is actively campaigning rather than testing the waters."

Bloomberg filed in early November to appear on the Democratic primary ballot in Alabama, initiating a 15-day process to formally file his candidacy with the FEC. He has also filed to appear on the ballots in Arkansas and Texas but does not plan to compete in Iowa or New Hampshire.

Bloomberg also recently announced a plan to spend $100 million on a digital campaign attacking President Donald Trump in battleground states, making him already one of the biggest spenders of the race despite his late entry.

Bloomberg’s filing comes roughly eight months after he initially announced he would not run for president and instead would focus his resources on combating climate change and gun violence.

"It’s essential that we nominate a Democrat who will be in the strongest position to defeat Donald Trump and bring our country back together. We cannot allow the primary process to drag the party to an extreme that would diminish our chances in the general election and translate into 'Four More Years,'" Bloomberg wrote at the time.

His stance has shifted in recent weeks, though.

"We now need to finish the job and ensure that Trump is defeated — but Mike is increasingly concerned that the current field of candidates is not well positioned to do that," his spokesman, Howard Wolfson, said in a statement to NBC News. "If Mike runs, he would offer a new choice to Democrats built on a unique record running America's biggest city, building a business from scratch and taking on some of America's toughest challenges as a high-impact philanthropist."