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By Bernd Debusmann Jr
BBC News, Washington
The Republican race is on to pick the party's next presidential candidate and televised debates will be staged to winnow a crowded field of hopefuls. The first such forum takes place this Wednesday - minus the contest's current frontrunner, Donald Trump.
At least seven candidates have so far qualified for the Fox News debate after meeting criteria set by the Republican National Committee.
The debate, held in Milwaukee, Wisconsin, is scheduled to begin at 21:00 EDT (01:00 GMT).
Here's what we know about the event and the contenders that made the cut.
Which candidates qualified?
To participate in the event, candidates have to meet a number of thresholds set by the Republican National Committee, including chalking up 40,000 individual campaign donations.
The candidates need to have at least 1% support in three separate national polls, or two national polls and one from an early presidential primary state such as Iowa. They must also sign a pledge to support the Republican party's eventual presidential candidate. Mr Trump has refused to sign the pledge.
At least seven candidates have said they qualify and plan to participate: Florida Governor Ron DeSantis, former United Nations ambassador Nikki Haley, ex-New Jersey Governor Chris Christie, North Dakota Governor Doug Burgum, entrepreneur Vivek Ramaswamy, South Carolina Senator Tim Scott and Mike Pence, former vice-president to Mr Trump.
Why won't Trump show up?
Mr Trump - whom opinion polls consistently place well ahead of his Republican rivals - has confirmed he will not participate in the debate.
"The public knows who I am & what a successful Presidency I had," Mr Trump said on his Truth Social platform on Sunday. "I will therefore not be doing the debates."
The former president added that recent polling demonstrates that he has "legendary" levels of support among Republican voters.
Instead of going to Milwaukee, US media have reported that Mr Trump has recorded a pre-taped interview with former Fox News host Tucker Carlson.
CBS, the BBC's US partner, has reported that the interview may air at the same time as the debates.
This could draw viewers away from Fox, which Mr Trump has called a "hostile network", saying it has not treated him fairly.
Does the outcome matter?
A poll released by CBS and YouGov last week shows that Mr Trump's already commanding lead over the other candidates has grown, even as he faced a fourth criminal indictment.
Some 62% of likely Republican primary voters say he is their preferred candidate.
But that does not mean the debate does not matter. The same CBS poll showed that a vast majority of likely voters - 91% - want the candidates to focus on making the case for themselves, rather than making the debate about Mr Trump.
Among the voters at least considering another candidate in addition to Mr Trump, about 50% said they are "waiting to see the debate". This could mean a potential boost for any participating candidates who are able to strike a chord with viewers.
Historically, it has often been the case that strong performance help candidates.
In the 2016 Republican election cycle for example, support for Mr Trump rose from about 24% on the day of the first debate to just over 30% by the time of the second one.
Another candidate, neurosurgeon Ben Carson, saw an even bigger opinion poll bump, jumping from 5.8% on the day of the first debate to about 20% at its sequel.
Whether or not any boost is enough to overcome Mr Trump's lead, however, remains to be seen.
How and where to watch?
The debate will be broadcast on all of Fox's platforms, including Fox News Digital, Fox News Audio and the Fox Business Network, as well as the media giant's streaming service, Fox Nation.
The event will last approximately two hours, ending at 23:00 EDT (03:00 GMT).
Is there another debate on the schedule?
The second Republican debate of the 2024 election cycle is due to take place on Wednesday, 27 September at the Ronald Reagan Presidential Foundation & Institute in Simi Valley, California.
Further details about the second debate will be released in the "coming weeks", according to Fox.