United States media have described Mr Steyer's campaign as the Democratic version of Mr Trump's; both men are political outsiders with vast personal wealth, running on the premise of changing the existing system.
"Americans are deeply disappointed and hurt by the way they're treated by what they see as the power elite in Washington, D.C., and that goes across party lines and it goes across democracy", Steyer said in a video his campaign was releasing Tuesday. The liberal advocacy organization had come under fire at the time from progressive activists and the Sanders campaign after the organization shared a video showing Sanders changing his campaign speeches to omit the mention of "millionaires" after Sanders became a millionaire himself through the sales of his 2016 book, "Our Revolution". "I'm Tom Steyer, and like you, I'm a citizen who knows it's up to us to do something", he says in his push for impeachment-an apparent attempt to convince listeners that his fortune doesn't alienate him from the Little Guy. "He's brought us to the brink of nuclear war, obstructed justice at the Federal Bureau of Investigation, and in direct violation of the U.S. Constitution, he's taken money from foreign governments, and threatened to shut down news organizations that report the truth", Steyer says in the ad.
Forbes lists Mr Steyer's net worth at $1.6bn (£1.2bn).
Sanders said in a statement that he liked Steyer personally, "but I do have to say as somebody who in this campaign has received received 2 million contributions, averaging $19 a person, I'm a bit exhausted of seeing billionaires trying to buy political power".
His late entry comes weeks after the first Democratic primary debates in Miami and about a week before the qualifying deadline for the second debates in Detroit.
His campaign must reach 1% in the polls or obtain donations from 65,000 donors, of which 200 must be from 20 different states.
He will instead be seeking re-election to the House of Representatives.
Joe Sestak, a former Pennsylvania congressman and three-star vice admiral in the US Navy, is another late start contender. His top issues - climate change and impeachment - haven't moved the needle for other candidates.
Shortly after Sanders's praise, Steyer told Business Insider that he admired Sanders's 2020 campaign describing him as "either the frontrunner or nearly the frontrunner".