The Ultimate Fighting Championship (UFC) is heading to the White House on Sunday, becoming the first ever professional sporting event staged at the US presidential residence.
About 4,300 people are expected at the invite-only mixed martial arts event on the South Lawn, with another 85,000 expected at a nearby fan zone.
A lawsuit failed to halt the event, but hot weather and thunderstorms forecast to sweep across the city on Sunday could dampen the spectacle.
The event coincides with President Donald Trump's 80th birthday, which is also Flag Day, and is part of celebrations for America's 250th anniversary.
The seven-bout card was arranged between Trump and his longstanding friend Dana White, UFC president.
The UFC spent about $60m (£45m) on the event, including $700,000 for grass repairs afterwards on a lawn that hosts the annual Easter Egg Roll.
The centrepiece is the "Claw" - a 92ft high metal structure that looms over the octagon and many of the seats. It weighs 600 tonnes.
A total of 14 fighters will compete in back-to-back fights, ending with the main card between Georgian-Spanish lightweight Ilia Topuria and American Justin Gaethje.
The action begins at 20:00 EDT (midnight GMT). It will be screened exclusively on Paramount+, which is run by Trump ally David Ellison. Last year, UFC signed a $7.7bn deal with the Netflix rival streaming service.
The ultimate winner may be UFC - making it to the White House is a fist-pumping brand boost for a sport that was once shunned by sponsors and venues and denounced as "human cockfighting" by a US senator.
The weather could cause delays during the event on Sunday, with thunderstorms forecast in Washington DC.
It's going to be a hot and humid day on Sunday in the nation's capital, with mid-afternoon temperatures peaking at around 91F (33C), according to forecasts.
As the heat and humidity builds, scattered thunderstorms are expected to develop through Sunday afternoon and into the evening, with the risk of lightning, downpours and wind gusts of over 50mph (80km).
The summer humidity in Washington often attracts an unpleasant number of insects.
A news conference for the event at the Lincoln Memorial on Friday was briefly delayed over "inclement weather" and fans were urged to seek shelter.
