Donald Trump has warned Florida's Governor Ron DeSantis against running for president in 2024, saying doing so would harm the Republican Party.
"I think he would be making a mistake. I think the base would not like it," the former president told Fox News.
He also threatened to release unflattering information about the 44-year-old, without providing details.
Both men have been tipped to announce presidential runs and become likely rivals for the Republican nomination.
Trump - a resident of the state - told reporters gathered outside a polling station earlier on Tuesday that he had voted for Mr DeSantis.
"I don't know if he is running. I think if he runs, he could hurt himself very badly. I really believe he could hurt himself badly," Mr Trump told Fox. "I don't think it would be good for the party."
If Mr DeSantis were to announce a presidential bid, Mr Trump said he would reveal "things about him that won't be very flattering - I know more about him than anybody - other than, perhaps, his wife".
He did not provide details - but Mr Trump has previously made threats to release damaging information about rivals.
He later described his potential opponent as "a fine guy" and denied there was a dispute between them. "There's not a tiff with me, and I'm way up in the polls," he said.
Mr DeSantis is a relative newcomer to politics but rose to national prominence after becoming Florida governor in 2019.
He has positioned himself as an enthusiastic champion of conservativism, and is considered by many to be the most likely candidate to supplant Mr Trump.
He is projected to defeat Democrat Charlie Crist and win re-election as Florida governor on Tuesday, a result that could serve as a platform for announcing a 2024 presidential bid.
Mr DeSantis has been tight-lipped about a potential presidential run but speculation has been rife. Mr Trump, meanwhile, said on Monday that he would make a "very big announcement" on 15 November.