"I think he's the most substantive candidate in the field and I think that he offers a unique approach both to the Democratic primary and ultimately, the election," Schoen said while appearing on "America's News HQ." Schoen also has served as an adviser to Bloomberg for years.
Schoen's comments came as President Trump predicted on Friday that Bloomberg wouldn't "do well" and would hurt former Vice President Joe Biden in the 2020 race. "Little Michael will fail," Trump said outside of the White House.
While Bloomberg has filed to run as a candidate in Alabama's Democratic primary, he has yet to make an official announcement.
Schoen said on Saturday that he was "all in" for Bloomberg, who won two New York City mayoral elections as a Republican.
"He has a unique appeal ... he's been a mayor, he's been a business leader, he's a philanthropist, he's got a progressive issue agenda of gun control, climate change, public health, education," Schoen said.
But, Republican strategist Kim Alfano described Bloomberg's strategy as "flawed from the getgo," noting that he wasn't planning on competing in Iowa or New Hampshire -- the first two states to hold nominating contests.
"If you can't play in those first two primaries, then the bus is going to leave you behind," Alfano said.
"The ball game really begins on Super Tuesday when about 40 percent of the delegates are at stake and that's when Michael Bloomberg has I think preliminarily ... decided to begin his campaign should he go forward," he said.