"Tom Steyer who, other than Mini Mike Bloomberg, spent more dollars for NOTHING than any candidate in history, quit the race today proclaiming how thrilled he was to be a part of the the Democrat Clown Show," Trump wrote on Twitter on Sunday. "Go away Tom and save whatever little money you have left!"
Steyer, whose net worth is estimated at $1.6 billion, spent approximately $252 million on his campaign, according to the Center for Responsive Politics.
Trump used Steyer's decision, which followed former Vice President Joe Biden's win in the South Carolina primary, to attack Biden's rival Mike Bloomberg, who is still in the race.
"I would find it hard to believe that failed presidential candidates Tom Steyer, or Mini Mike Bloombeg, would contribute to the Democrat Party, even against me, after the way they have been treated - laughed at [and] mocked," Trump wrote on Twitter on Sunday. "The real politicians ate them up and spit them out!"
Steyer responded a few hours later.
"Donald, I'm prepared to do whatever it takes to beat you and save our democracy," he wrote on Twitter.
During the 2016 election, Steyer gave about $65 million to support Democratic candidates and environmental causes, according to Forbes.
Steyer dropped out right before Super Tuesday, when voters in 14 states will go to the polls for primary elections and American Samoa will have its caucus.