Donald Trump has amped up his attacks on Ron DeSantis -- making some of his harshest public comments yet directed at Florida's governor and potential GOP campaign rival.
"You have to remember Ron was a disciple of Paul Ryan, who is a RINO (Republican In Name Only) loser," Trump said to a crowd in Davenport, Iowa on Monday, attempting to cast DeSantis -- a founding member of the House Freedom Caucus in Congress -- as a pre-MAGA Republican who opposed ethanol and supported cuts to Medicare and Social Security.
"Romney -- I'm not a big fan of Mitt Romney, lost his election and to be honest with you, Ron reminds me a lot of Mitt Romney," he said.
Trump then appeared to speak directly to DeSantis: "So, I don't think you're going to be doing so well here. But we're going to find out."
DeSantis has not yet declared his candidacy for a White House bid despite recent tours of pivotal early voting states like Iowa and Nevada, though he's privately indicated to allies he intends to launch his candidacy in May or June, sources familiar with his plans told ABC News.
DeSantis is considered maybe Trump's chief rivals should he enter the race as he trails the former president's favorability ratings only slightly in a recent Des Moines Register's Iowa Poll.
During Trump's speech -- which sources familiar with the matter had said would be focused on education -- he vowed to cut funding for any school that is pushing critical race theory or what he called "transgender insanity," or that has a vaccine or mask mandate. He also again said he would support the direct election of school principals by parents, and vowed to break up the Department of Education if elected.
DeSantis did not comment directly on Trump's attacks but released a tweet following the remarks, where he addressed education by disavowing "political indoctrination" in universities.
"The publications said Trump still has really high approval ratings with the Republican voter base is defeating Ron DeSantis in poll after poll by a lot and I'm beating Joe Biden by a lot– very important," Trump said.
The former president on Monday focused directly on DeSantis' record as a former member of Congress and dove into other stances the governor has taken.
Trump attacked DeSantis over his previous support -- while serving in Congress in 2017 -- of a bill that would have immediately ended the Renewable Fuel Standard, or the RFS. The RFS mandates that specific percentages of ethanol -- a major industry in Iowa -- be part of the nation's fuel supply.
"Okay, so remember this -- Ron Desanctus. Did anyone ever hear of Desanctus? Desanctimonious ... Ron Desanctus strongly opposed ethanol. Do you know that? And we don't even know if he's running but I might as well tell you. If he's not running, I'll say he was fine on ethanol, don't worry," Trump said in his speech.
"He strongly opposed ethanol and fought against it at every turn. And he's gonna do that again. Because people that come out early for something, that's where they go. Politically, but he was very, very bad on ethanol," he said.
Ethanol is a key issue for many of Iowa's farmers. Trump himself has faced criticism from farmers while president because he granted ethanol waivers to some small refineries, giving them an exemption from blending ethanol into their fuel. Trump, however, billed himself as the "most pro-farmer president," on Monday.
The former president also continued to attack DeSantis over his positions on Social Security, saying he "wanted to decimate it and voted against it."
"A lot of people don't know that. I think they've been finding out over the last four weeks. One of the reasons that we're zooming in the polls, perhaps," Trump said. "He also voted to severely cut Medicare. I will not be adding Medicare and I will not be cutting Social Security."
Trump did not mention GOP opponent Nikki Haley's recent calls for changing the retirement age for Americans currently in their 20s and limiting Social Security and Medicare benefits for wealthy Americans.
The former South Carolina governor first proposed the entitlement program changes and change of retirement age for "young people" at a town hall in Iowa last week.
Haley had the highest uncertainty in the recent Des Moines Register Iowa Poll, with 40% of Republicans surveyed saying they do not know enough about her, while garnering a 53% approval rating.
Trump also addressed DeSantis' with a group of reporters on en route to Davenport, Iowa on Monday, the same town DeSantis toured on Friday.
Trump said he regretted endorsing DeSantis for governor in 2018, saying, "This guy was dead. He was dead as a doornail … I might say that," Trump told Politico.
"I said, 'You are so dead right now you are not going, no endorsement is going to save you. George Washington won't save you.' He said, 'I'm telling you, if you endorse me, I have a chance,'" Trump said.
Politico also reported that Trump has been workshopping nicknames for his potential rival, but he said that he has decided against attacking DeSantis with the name "Meatball Ron," calling it "too crude."
ABC News' Olivia Rubin contributed to this report.