The sport once bemoaned by Sen. John McCain as “human cockfighting” is about to take over the South Lawn of the White House on Flag Day.

The 30-year journey from barely regulated bloodsport to multibillion-dollar operation culminates in the greatest spectacle in mixed martial arts history with UFC Freedom 250 on Sunday night.

The one-of-a-kind event went with a tighter slate of fights — seven, rather than the 12 to 14 typically scheduled for the dozen or so major events each year. That means only 14 men will have the distinction of having competed in professional combat sports at the home of the President of the United States.

“It’s a massive opportunity, so I feel really blessed,” Bo Nickal, a middleweight who will face Kyle Daukaus, told The Post this week. “To be able to go compete at an event like this is such an honor, so I feel like I put a ton of effort into this [training] camp, and I want to make sure that I put on a good performance.”

The event is headlined by a pair of championship fights. Lightweight champion Ilia Topuria and interim champ Justin Gaethje will vie for the unified championship at 155 pounds in the main event. Immediately preceding that, Alex Pereira and Ciryl Gane square off for the vacant interim heavyweight crown.

Of the four, only Gaethje is a born-and-raised American. He’s one of eight representing the U.S., and a crowd of mainly military service members serves as extra motivation for the heavy-hitting crowd pleaser from Colorado.

“The way that I fight, people love it,” Gaethje told The Post in the lead-up to the fight. “I really capture people’s emotions, and I’m going to do the same thing [in] this fight.

“Fighting in front of the military is so special for me. I constantly use my name to try to … raise as much money and be as positive and influential towards the people that sacrifice their well-being for my opportunity to do something like this.”

As thrilled as they are to compete on such a unique stage, with the front columns of the White House as a backdrop, some such as Michael Chandler are doing their best to focus on the task at hand. In his case, that’s knocking out lightweight opponent Mauricio Ruffy before the same can be done to him.

“It’s really cool. It’s one of those deals where I try not to think about it too much and think about the bigness, the massiveness, the weight of the moment because you can really psych yourself out of this whole thing and the moment becomes too big,” Chandler told The Post. “Ultimately, I got four-ounce gloves on, I got a mouthpiece, and we’re in an Octagon, just like I’ve done it seven other times in the UFC.”

The six fighters on the fight card who hail from beyond U.S. borders still feel the weight of the moment, including one of them who’s on the cusp of history.

Pereira, a native of Brazil, is the first fighter in UFC history to even attempt to capture a championship in a third weight class, having previously earned the middleweight and light heavyweight belts before endeavoring up to heavyweight for the first time.

Having moved to Connecticut to train, his family now calls the U.S. home, and he’s been grateful for the opportunities this country has given him — including a visit to President Trump in the Oval Office last month.

“Very special to be there, to be next to the president,” Pereira told The Post through an interpreter the following day. “… How many fighters wanted to be there, and I was one of few people that had an opportunity to be a part of it.”