"It's disgusting that Ron DeSantis is launching his general election campaign with racist dog whistles," said Florida Democratic Party Chair Terrie Rizzo.
David Turner, a spokesman for the Democratic Governors Association, called DeSantis "a desperate candidate who will stoop to new lows in order to court and give voice to fringe elements of society."
DeSantis spokesman Stephen Lawson brushed off the criticism.
"Ron DeSantis was obviously talking about Florida not making the wrong decision to embrace the socialist policies that Andrew Gillum espouses," he said in an email. "To characterise it as anything else is absurd."
Trump also went on the attack. On Twitter hours after the primary he called Gillum a "a failed Socialist Mayor" and claimed he has let crime and other problems "flourish" in Tallahassee.
DeSantis defeated a more mainstream conservative Republican, Agriculture Commissioner Adam Putnam in yesterday's primary.
Gillum defeated former Representative Gwen Graham in an upset that made him the most high-profile 2018 primary candidate to win with the endorsement of Bernie Sanders, a liberal Vermont senator who ran for president in 2016.
Florida is a closely divided swing state in national politics. Trump won there by 1 percentage point in 2016, as did Democrat Barack Obama in 2012.
The state is a microcosm of what's at stake in 2018.
In play in November is not just a governor's mansion in the nation's third largest state that holds the keys to redistricting over the next decade.
There's also a Senate race that could be pivotal in the battle for which party controls the chamber, a series of House races important to Democrats' hopes of taking the majority, and a signal of what's the come in 2020 in a state that has picked the president in all but one election since 1964.
Gillum campaigned on gun control, overhauling the criminal justice system and making healthcare a right. His defeat of Graham, who ran as a moderate and was the favourite leading up to the election, was a stunning upset. He also had the backing of billionaire activist Tom Steyer, who is leading a drive to support Trump's impeachment.
"We have the ability to bring together the Bernie Sanders wing, the Hillary Clinton wing and the Barack Obama wing of the Democratic Party and quite frankly move forward a collective universal vision in this state that is going to allow us to win," Gillum said on CNN.
Gillum likely will have to confront Republican attacks on his record as mayor. The FBI has started a corruption probe into his city, though he hasn't been publicly implicated in the investigation.
DeSantis has staked out down-the-line conservative positions, calling for halting illegal immigration, defending gun rights and restricting abortion. Putnam also ran as a conservative, but it wasn't enough.
"Putnam had the money, he had the Chamber of Commerce Republicans behind him, but he couldn't compete with President Trump's endorsement," Dan Eberhart, chief executive officer of Canary Drilling Services and a DeSantis backer, said in an email. "That has to send a strong signal to establishment Republicans that the president remains highly popular and influential."
In the Senate primary, Scott easily won the Republican nomination to run against incumbent Sen. Bill Nelson in November, a race that will be pivotal in determining the balance of power in the chamber.
