The Republican candidate for president was heckled in Jacksonville, where hundreds gathered on Sunday to remember the three victims of the attack.
He was forced to step back from the microphone before a member of the city council asked the crowd to listen.
"It ain't about parties today," Ju'Coby Pittman said, adding: "A bullet don't know a party."
Mr DeSantis, 44, who has loosened gun laws in the state and faced criticism from civil rights leaders for targeting what he calls "woke ideology", eventually spoke and called the gunman a "scumbag" which prompted applause from some of the crowd.
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Around 200 people attended the vigil, which took place in a predominantly black area just yards away from the Dollar General shop where the shooting happened the previous day.
Twenty-one year old Ryan Christopher Palmeter fired eleven rounds at 52 year-old Angela Carr who was sitting in her vehicle, before entering the shop and shooting another two people dead.
Anolt Laguerre Jr, 19, worked at the Dollar General and was killed as he tried to flee.
Jerrald De'Shaun Gallion, 29, was shot dead as he entered the premises. Another woman was chased but managed to escape.
As police arrived, the attacker turned a gun on himself and died at the scene. An AR-15 semi-automatic rifle and a Glock handgun, both legally obtained, were used in the shooting.
Police have said the gunman was motivated by racist hatred.
"He knew what he was doing. He was 100% lucid," Sheriff T K Waters told reporters. "Finely put: this shooting was racially motivated and he hated black people."
He left behind racist messages, police said, which read like "the diary of a madman".
The gunman was detained for 72 hours in 2017 under mental health legislation that allows the involuntary detainment of an individual for treatment. He was released after the examination, police said, which is why it did not appear on his background checks when purchasing the guns.
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Mr DeSantis said financial support would be provided to bolster security at the historically black Edward Waters University, near to where the shooting happened.
The gunman first went to the university campus, where he was asked to identify himself by a security officer. When he refused, he was asked to leave. He was then seen putting on a bullet-resistant vest and a mask before leaving the area.
"What he did is totally unacceptable in the state of Florida," Mr DeSantis said. "We are not going to let people be targeted based on their race."
Bishop John Guns, referring to Mr Gallion, told the crowd: "In two weeks I have to preach a funeral of a man who should still be alive. I wept in church today like a baby because my heart is tired. We are exhausted."
The shooting fell on the 60th anniversary of the March on Washington for civil rights, where Dr Martin Luther King Jr gave his famous 'I have a dream' speech.
President Joe Biden, during remarks on the anniversary on Monday, called the shooting an "act of domestic violence extremism".
"Domestic terrorism rooted in white supremacy is the greatest terrorist threat we face in the homeland," Mr Biden said.
The president also renewed calls for a ban on assault weapons and high-capacity magazines.
US Attorney General Merrick Garland earlier said the shooting was being investigated as a hate crime.