WASHINGTON — Thousands of UFC fans, liberal protesters and supporters of President Trump descended on the White House Sunday evening as the commander in chief prepared to celebrate his 80th birthday with a seven-fight card on the South Lawn.

Trump and about 4,000 ticketed guests have reserved seats in the custom-made “Claw” — a steel lighting, camera and tarp overhang that dwarfs the adjacent executive mansion — while up to 120,000 ticketed guests will be able to watch the contests on the Ellipse just to the south.

Mixed martial arts fans rushed toward checkpoints to enter the watch party while chanting “U-S-A! U-S-A!” ahead of the first bout at 8 p.m. — while protesters manned port-a-potties and invited passersby to wish the president a “crappy birthday.”

While a federal judge cleared the fights to go ahead by dismissing a last-ditch lawsuit Friday afternoon, Mother Nature could still throw a wrench in proceedings, with showers and thunderstorms forecast across the national capital region during the evening.

The spectacle, dubbed UFC Freedom 250 in a nod to the upcoming 250th anniversary of the Declaration of Indpendence, was available to stream on Paramount+ — but that wasn’t enough for many hardcore fans.

“We left at like 2:00 in the morning. None of us could sleep, we were so buzzed about this,” said Kellen Drury, 27, of Altoona, Pa., who arrived in DC with three friends despite not being able to score tickets to either the watch party or main event.

“It was still worth the trip just to be here. It’s like being outside the Super Bowl,” Drury told The Post.

“People are gonna bitch and moan about the cost, they’re gonna call it tacky, they’re gonna speak out against the brutality of the fighting itself. But even the haters are gonna watch it because that’s what Donald Trump’s all about, making it too hard to look away.” 

“I tried to get my wife to come with me, but she had no interest in spending the weekend with UFC fans, and no interest in being around political hotheads on the right or the left,” said UFC fan Darius Boone, 43, of Prince George’s County, Md.

“I’m just here because I’m a fan and nothing like this has ever been done before,” Boone added. “Plus, it’s celebratory. I mean, come on, we’re celebrating a major milestone in the history of our country.

“Really, what’s more American than a $60 million claw on the White House lawn?”

“How many times do you get a chance to see something that’s never been done before, especially something so ridiculous?” agreed Nolan Haugen, 34, of Fargo, ND. “It’s like bringing Las Vegas to DC!”

“Of course I had to see it — just to say I was here,” he added. “I’m not even that big a fan of the UFC, although I’ll admit I’m a fan of the president. Happy birthday President Trump!” 

DC local Nadia Rahman, 36, slammed the event as “completely tasteless.”

“It is historic, in its own way, because nothing else Trump has done in either term quite encapsulates who he is in one swoop. It’s strangely comical, except nothing about what I’m seeing is the least bit funny. It’s just like Trump’s ballroom,” she said.

The National Park Service said in a court filing Tuesday that the UFC and its sponsors had spent “well over $60 million and tens of thousands of hours of labor” on the event. The NPS was responding to a lawsuit from the liberal Public Integrity Project, which alleged the fights amounted to a “corrupt use of our most sacred national monuments for private gain.”

Mark Shapiro, president and chief operating officer of UFC parent company TKO, told The Hollywood Reporter earlier this month that “we will not be making money on America’s 250th anniversary. This is an investment for the long term. This is about earned media.”

“We see this once-in-a-lifetime stage as a strategic investment to drive subscriber acquisition at Paramount+, massive audience sampling for the UFC overall and Super Bowl-like earned media across the globe.”