Analysts say a Bloomberg candidacy could do the most damage to the prospects of frontrunner Joe Biden, but the former vice president put on a brave face Friday and said he was not worried Bloomberg would draw away centrist voters.
Bloomberg's name was posted among 17 candidates on the Alabama Democratic Party's website only hours before registration closed.
Alabama is not one of the early primaries but it has the earliest deadline to register.
Biden, who will also turn 77 on November 20, has placed himself in the political center with South Bend Mayor Pete Buttigieg, while Vermont Senator Bernie Sanders and Massachusetts Senator Elizabeth Warren run to his left.
"Michael's a solid guy," Biden told reporters in Concord, New Hampshire, while registering to take part in the February primary in the northeastern state.
"I have no, no problem with him getting in the race," Biden said. "And in terms of he's running because of me, last polls I looked at I'm pretty far ahead.
"If I'm not mistaken I'm doing pretty well, both relative to Trump and relative to all the people running," he said.
Jason Mollica of American University said the entry of Bloomberg in the race could be "an indication that he believes the Democrats do not have a strong candidate that can defeat President Trump."