MIAMI — Florida billed itself as a coronavirus oasis when it wooed the Republican National Convention: The pandemic seemed under control, and Republican state and city leaders welcomed a major televised event to show off the progress and cement votes for President Trump in the nation’s biggest presidential battleground.
That pitch collided with the grim reality of the coronavirus and its explosive surge in Florida when Jacksonville, the convention’s new host, imposed a requirement on Monday that people wear masks indoors, precisely the mandate that the Republican Party had hoped to avoid for its celebrations.
The mask order is almost certain to rankle Mr. Trump, whose demands for a traditional, packed rally forced the move earlier this month to Jacksonville from Charlotte, N.C., in the first place.
The resurgence of the virus in Florida, where the number of new cases has been rising nearly every day, has turned the convention into an even riskier gamble. In a must-win state for Mr. Trump — and arguably a must-win city for Republicans — recent polls have shown that Jacksonville residents do not want the convention.
Masks will be required in indoor public places and in any other gathering spots where social distancing is not possible, Jacksonville officials said. It is unclear how long the mask order will be in place, but it will presumably apply to the 15,000-seat VyStar Veterans Memorial Arena, where three nights of convention speeches, including Mr. Trump’s, are scheduled for Aug. 24-27.
The president has refused to wear a mask himself, even as the nation’s top doctors have emphasized that facial coverings are critical to slowing the virus. Vice President Mike Pence has recently worn masks in public, including over the weekend in Texas, and encouraged other people to do the same.
In a telling move, Mayor Lenny Curry, a Republican, who had lobbied for the convention and resisted a mask requirement, was absent from Monday’s announcement. His spokeswoman said he had a prior family obligation.
“We are still two months out from that event,” he said last week. “In the meantime, we have to focus on what’s happening in the city and what we can control.”
His administration’s policy reversal came after a morning conference call with local hospitals. Duval County, which includes Jacksonville, is now averaging about 384 new cases of the virus a day. Two weeks ago, that figure was 32.
In a statement, the Republican National Committee said it would comply “with local health regulations in place at the time.”
“The event is still two months away, and we are planning to offer health precautions including but not limited to temperature checks, available P.P.E., aggressive sanitizing protocols, and available Covid-19 testing,” the statement said.
Mr. Trump did not immediately respond to the announcement. But as he has pushed states to reopen their economies, he has shown an ability to bend local regulations to his will. Officials in Tulsa, Okla., rescinded a curfew ahead of the president’s rally there earlier this month after Mr. Trump said on Twitter that he had discussed the curfew with the mayor, a Republican.
Democrats say Republicans want to use the convention to shore up votes in Northeast Florida.
“Jacksonville — Duval County — is a swing city in a swing state,” said State Senator Audrey Gibson, the Democratic majority leader, who represents the city. “Duval County went blue in the last election. So it’s pretty obvious what this is about.”
In 2016, Mr. Trump won Duval County by a mere 5,968 votes, though Hillary Clinton never campaigned there. In 2018, the county voted for Andrew Gillum, a Democrat, for governor, though its surrounding suburbs remained deeply red.
Jacksonville’s broad television market includes Republican suburbs like affluent St. Johns County, home to St. Augustine — the type of place where Democrats hope to win over enough white, college-educated women to remain competitive in November. Former President Barack Obama won Florida twice in part by keeping vote margins close in Duval County. (For the newcomers: It is pronounced “DOO-val.”)
In addition to dealing with virus this year, Jacksonville has also become a microcosm of how the nation has been forced to confront systemic racism in the wake of George Floyd’s killing. African-Americans make up nearly a third of Jacksonville’s population of 912,000 but have been historically excluded from power in local government.
That Jacksonville — a city perennially overshadowed by Miami, Orlando and Tampa that under normal circumstances might never have held a convention — gets its moment in the political spotlight while it grapples with the virus and the unfulfilled promises to its African-American residents has raised the stakes for local leaders. What amounts to a massive campaign rally for a divisive president may only lead to more contagion and unrest.
“As far as the R.N.C. is concerned, that took us a hundred steps backwards,” said Moné Holder, senior program director for New Florida Majority, one of the social justice organizations that participated in protests against police brutality. “The powers that be try to paint it as, ‘one city, one Jacksonville’ — I think that’s the quote the mayor likes to use — but it’s very, very divided, racially and economically.”
A online poll of 2,524 registered Duval County voters released last week by the Public Opinion Research Lab at the University of North Florida found that 58 percent of respondents opposed hosting the convention, with 71 percent concerned that it would lead to virus spread, and 61 percent worried that it would result in unrest. Only 39 percent approved of Mr. Trump’s performance in office.
But Mr. Trump has an affinity for Florida, his adopted home, and found an eager ally in Gov. Ron DeSantis, a Republican, who is said to have ambitions for higher office. Mr. DeSantis has talked about the convention’s “massive economic impact” as its chief draw.