Pallade Veneta - Red and blue America square off in clash of the governors

But Republican Florida governor Ron DeSantis and Gavin Newsom, his counterpart in Democratic California, will swap social media antagonism for an in-person televised debate Thursday that could be preview the White House race in 2028.

The pair represent almost one in five Americans -- California is the largest US state and Florida is third -- and debate host Fox News is billing the showdown as a clash between liberal blue and conservative red America.

The right-leaning cable network says the debate will focus on the "vastly different approaches" of the governors to issues from the economy and immigration to crime -- though both Newsom and DeSantis have broader goals.

The Florida governor, once seen as the most viable alternative to scandal-plagued Donald Trump for Republican presidential nomination, is desperate to revive a flagging White House bid going into election year.

Newsom, 56, isn't running but speculation about a presidential campaign in 2028 has grown as commentators have been impressed with his appearances on the stump for President Joe Biden.

"This is a high school version of American Idol," Republican strategist Brian Robinson told The Atlanta Journal-Constitution ahead of the debate.

"It makes no difference for 2024, but it's a chance to spot talent for a future presidential race."

Newsom has spent much of the election cycle needling DeSantis over gun control, abortion restrictions and other so-called "culture war" issues such as the teaching of gender and sexuality in classrooms.

- 'Shadow campaign' -

"Freedom, it's under attack in your state," Newsom said in an ad that aired in Florida last year.

"Republican leaders, they're banning books, making it harder to vote, restricting speech in classrooms, even criminalizing women and doctors."

DeSantis has fired back at Newsom on immigration, public health restrictions and crime, arguing that "leftist policies" have damaged Californian cities like San Francisco and have sparked an exodus to conservative states.

"He caters to a very far-left slice of the electorate. I think that that will be on display when we have the debate," DeSantis said at a campaign event in Manchester, New Hampshire last week.

"But I've been warning Republican voters, it may not be Biden in 2024. This guy is running a shadow campaign. He denies it, but even people in his own party are saying it."

The 90-minute "DeSantis vs. Newsom: The Great Red vs. Blue State Debate" takes place in the suburbs of Atlanta, Georgia, a once staunchly Republican state that has moved leftwards to become a key battleground.

There has also been bad blood between the pair over DeSantis transporting undocumented migrants to California, and Newsom's fierce criticism of Florida's six-week abortion ban.

Newsom called DeSantis a "small, pathetic man" and suggested that Florida officials could face kidnapping charges for their involvement in a stunt flying migrants from Texas to Sacramento in June.

DeSantis appears to face more risks on the night, although political scientist Justin Buchler, of Case Western Reserve University in Ohio, told AFP that either governor could slip up in the debate arena.

"They each have political ambitions, which would be set back by an embarrassment, so this is a bad deal for each," he said. "They can only lose."

L.Guglielmino--PV