Trump made fun of Bloomberg's height calling him "mini Mike" before accusing him of being against farmers.
He was in California to sign a Presidential Memorandum on Developing and Delivering More Water Supplies.
"Mini Mike hates the farmer.
Long before we learned of his hatred of the farmer and the disrespect of the farmer.
So I don't know I don't think he's going to be the candidate anyway to be honest," said Trump to his supporters.
Trump made the remarks before signing an order to bring more water to Californian farmers and just a few hours ahead of Bloomberg's high-risk debut on the Democratic debate stage in Nevada.