Chief U.S. District Judge Mark Walker also made the rare move of putting Florida under a process known as "preclearance," meaning that he will have to approve any changes to certain provisions to the state's elections laws.

The state "has repeatedly, recently, and persistently acted to deny Black Floridians access to the franchise," the judge wrote.

Walker's 288-page decision came in a lawsuit challenging a 2021 law that imposed new restrictions on mail-in voting and third-party voter registration organizations. DeSantis and Republican legislative leaders quickly slammed Walker's ruling and vowed to appeal.

DeSantis and GOP lawmakers pushed the election-law changes after former President Donald Trump and his supporters hammered on unfounded allegations of widespread fraud in Trump's 2020 election loss to Democrat Joe Biden.

The law passed after DeSantis and other Republican officials praised the relatively smooth election in Florida, where Trump won by a comfortable margin.

The law also came after the number of Black Floridians who voted by mail doubled amid the coronavirus pandemic in 2020.

The legislation (SB 90) included restricting election supervisors' use of drop boxes; requiring voters to request mail-in ballots more frequently; and forcing third-party groups to provide a disclaimer informing potential voters that their applications may not be turned in within a 14-day window imposed by the law.

The League of Women Voters of Florida and a number of Black and Hispanic advocacy groups filed lawsuits challenging the measure, alleging that it was an effort to restrict minority voters from accessing the ballot. Walker held a two-week trial early this year.

In Thursday's ruling, Walker found that "every single challenged provision has a disparate impact on Black voters in some way."

Walker wrote that the main question was whether the legislation was enacted "without regard to whether it harmed minority voters" or whether it targeted minority voters to secure an electoral advantage for Republicans over Democrats.

The judge noted that the law was not intended to discriminate against Hispanic voters, who are not as strongly associated with either the Democratic or Republican parties.

"In sum, this court concludes that to the extent promoting voter confidence or preventing fraud may have motivated the Legislature in part, this court finds that the Legislature passed SB 90 with the intent to restructure Florida's election system in ways that favor the Republican Party over the Democratic Party. This court further finds that, to advance the Legislature's main goal of favoring Republicans over Democrats, the Legislature enacted some of SB 90's provisions with the intent to target Black voters because of their propensity to favor Democratic candidates," Walker wrote.

The provisions that were intended to discriminate against Black voters violate the federal Voting Rights Act, Walker ruled. The judge also decided that the Legislature would not have passed the provisions "absent an intent to discriminate against Black voters," a violation of the 14th and 15th Amendments.

The temptation is great "for the party in the majority to target the particular racial groups that support the minority party," especially in Florida, where elections are won by razor-thin margins, Walker wrote. Republicans hold super-majorities in the state House and Senate.

"The evidence before this court also shows that, for the past 20 years, the Legislature has given into that temptation by repeatedly targeting Black voters because of their propensity to favor Democratic candidates," the judge wrote.

In explaining his decision to put Florida under preclearance restrictions, Walker pointed to a measure passed by the Legislature this month that would impose new restrictions on mail-in voting, while repealing the disclaimer requirement in the 2021 law.

Litigation over election law takes time, Walker wrote.

"And so, before litigation can run its course, the Legislature can merely change the law — as it has done here (with the new law). The result is that Floridians have been forced to live under a law that violates their rights on multiple fronts for over a year. Without preclearance, Florida could continue to enact such laws, replacing them every legislative session if courts view them with skepticism. Such a scheme makes a mockery of the rule of law. Under any metric, preclearance is needed," he wrote.

The preclearance requirement bans Florida from enacting any law or regulation dealing with third-party voter registration groups, drop boxes or "line warming," a term used when people or groups hand out drinks or food to voters waiting in line, for the next 10 years.

During a news conference Thursday afternoon in Palm Beach County, DeSantis told reporters that Walker's ruling "was not unforeseen because we typically set our clocks to getting a partisan outcome in that court."

DeSantis, a Harvard Law School graduate, predicted that Walker's decision would be overturned by the Atlanta-based 11th U.S. Circuit Court of Appeals.

"There's an old saying in law, if you have the facts, on your side, argue the facts. If you have the law, on your side, argue the law. If you have neither you pound the table. Well, this is a judicial equivalent of just pounding the table, and I think it was performative partisanship," the governor said.

In a prepared statement, Senate President Wilton Simpson called the judge's ruling "appalling."

"This order is highly unprofessional, inaccurate, and unbecoming of an officer of the court. The Florida Senate looks forward to continuing to advocate for fair, free, transparent and secure elections for all," Simpson, R-Trilby, said.

House Speaker Chris Sprowls also blasted the decision.

"The illogical leaps and unsupported inferences in Judge Walker's opinion amount to a 288-page accusation of discriminatory intent based on limited analysis of data he thinks the Legislature might have had, the uncritical and complete acceptance of the comments of Democratic lawmakers and a total disregard for other viewpoints," Sprowls, a Palm Harbor Republican who is a lawyer, said.

Florida lawmakers knew that the 2021 measure would have a disparately negative impact on Black voters before they passed it, Walker wrote.

"The evidence before this court not only suggests that the Legislature had such knowledge, but also that it specifically sought it out," he said.

Walker's order bans state and local elections officials from enforcing the challenged provisions of the 2021 law.

The ruling chronicled what Walker described as the state's "grotesque history of racial discrimination," saying that "when all of the evidence is viewed together, a coherent picture emerges."

"What is this court to make of this history? To be sure, there are those who suggest that we live in a post-racial society," wrote Walker, who was appointed to the bench by former Democratic President Barack Obama. "But that is simply not so. Still, this court is mindful of the Eleventh Circuit's admonition that Florida's racist history cannot ban 'its legislature from ever enacting otherwise constitutional laws about voting.' … But Florida's painful history remains relevant; it echoes into the present and sets the stage for SB 90."

— News Service staff writer Jim Turner contributed to this story.