Sergeant Major Bob McDonald — an actor, singer in the U.S. Army Chorus and frequent national anthem performer around town — is a minor celebrity among D.C. sports fans. He gets recognized in arena concourses and written about by local blogs. An Uber driver recently asked him to pose for a selfie. He still describes himself as just a local sports fan who uses his voice to watch his favorite teams play up close, but if you do this job as long and as well as McDonald has, maybe your status will change a little bit.

And so it was that McDonald showed up at a Northwest D.C. house party Saturday night, set to surprise dozens of hockey-loving strangers.

“When he showed up, you’d think Elvis had arrived at the door,” said Tracey Madigan, one of the hosts of the party. “It was ‘OH MY GOD I CAN’T BELIEVE HE’S HERE. Everybody was screaming. … He was treated kind of like a rock star.”

McDonald doesn’t regularly play house parties, and he never leaves a Caps game early. He made an exception in this case, for a party in honor of Madigan’s recent naturalization ceremony.

Okay, let’s back up. Madigan and her husband, Richard Latendresse, are Montrealers who moved to D.C. for journalism work in 2006. This was supposed to be a brief two-year stay, followed by a return to Canada. Like so many of us who planned to come and go, they’re still here. And with Latendresse covering the White House for the French-language TVA, and with a return still not imminent, they decided last year to become American citizens.

This is a complicated process, and Madigan wound up reaching the finish line first. She was naturalized at a local courthouse in January, and planned a party with dozens of friends to celebrate the occasion. Now, she and her husband are both fans of the Canadiens, but you live in a place long enough and lines start to blur. So they now share Caps season tickets, and consider themselves supporters of both franchises. They never felt much of a Montreal-D.C. rivalry, and the Caps, as Madigan told me, are “easy to love.”

So one of their hockey-mad friends, Diana Hosford, happens to be close with McDonald. He had recently earned widespread plaudits for singing the Canadian anthem in French before a Caps-Canadiens game, and Hosford suggested inviting him to the party and asking him to sing the anthem. “That would be incredible,” Madigan said. But it turned out the Caps were hosting the Ducks on that night, and McDonald has a policy: If he sings an anthem, he stays to watch the game.

That’s where Madigan left it. But Hosford and McDonald kept talking. Hosford works for TAPS — a group that works with surviving family members of fallen Armed Forces members, and that has worked closely with the Caps.

“She’s the kind of person who never asks for anything,” McDonald said. “So I was like ‘Yes, I am doing this for you.’ So I did the unthinkable: I sang the anthem at Verizon Center and I gave my tickets away.”

He headed straight from the game to their home, still wearing his Caps sweater. All he knew of Madigan and Latendresse was that they were becoming American citizens. He didn’t know what he was going to sing, what the crowd would be like, what sort of reception he would receive. He didn’t know if people would know or care who he was. Turns out they did.

“It was a party full of D.C. sports fans,” Hosford said.”I think when he walked in, everyone was like ‘Oh my God!’ ”

“He’s a household name,” Madigan said. “It was like Elvis, I’m telling you.”

“I was kind of embarrassed,” McDonald said. “I was like ‘okay, I’m, like, an anthem singer. I was sort of looking behind me, like, ‘Is someone behind me? What’s going on?’ ”

This is where we go back even further. McDonald, who grew up in McLean, got into anthem singing after he graduated from Oberlin. He was working at Tower Records at the time, was obsessed with sports, and didn’t have enough money to buy Caps or Bullets tickets. The anthems got him a seat, and then became something more. He’s in his 24th year doing anthems; now, he gets pre-game fist bumps from T.J. Oshie and a pre-game salute from Barry Trotz, gestures that haven’t gotten old. (“At the end of the day, I’m still a fan,” he said. “I look at these players like I’m a little kid.”)

“It’s just turned into really one of the coolest things that I do,” he said. “It’s just been a wonderful, wonderful layer of my performing life. I never imagined it would be this.”

Meanwhile, thousands of Verizon Center regulars feel “warm and fuzzy” when they hear his voice, as Madigan put it. When you see someone like McDonald or Caleb Green or D.C. Washington year after year after year, you actually do start to think of them as acquaintances. They become part of the communal experience of going to these games, a piece of the fabric that wraps life in Washington a little closer around your skin. Not to get mushy, but this is the thing I like most about Washington sports teams: They’re communal touchstones in a place that doesn’t always have many of ’em; they offer normal routines that don’t get flipped every four or eight years.

So here this couple was, surrounded by their Caps-loving friends, putting a D.C. stamp on their next step. First, McDonald sang Oh Canada; “I never knew the Canadian national anthem would make me cry,” someone said in the back. Then, with Madigan chanting “USA,” he sang the Star Spangled Banner, encouraging the crowd to sing along. They did, naturally adding the RED and OH screams heard at Caps games. It all worked.

“I have heard Bob sing in front of thousands of people many times; it was never more powerful than it was in that room,” Hosford said.

“I just thought it was a privilege that we got to be serenaded by him, by a compatriot,” Madigan said. “Everyone was touched.”

“There I was, singing the anthem in this home in the Palisades to these two wonderful people I’d never met,” said McDonald, whose wife happens to be a naturalized citizen. “It just makes you think about your own citizenship, and how you would never take it for granted when you witness something like this.”

McDonald stuck around the party after his performance; the family’s kids were performing with their band, and he didn’t want to miss seeing some live music. The neighborhood was later buzzing about this whole night, and Madigan couldn’t have been more thrilled.

“He was the real deal, to show up on his personal time, on a Saturday night. I just thought it was so generous of him, and it was very symbolic for us, symbolic of the openness we’ve felt since we’ve been here,” she said. “It literally made the evening.”

(Coincidentally, McDonald and his band are doing a Frank Sinatra show Wednesday at the Kennedy Center’s Millennium Stage. The event, which is free and open to the public, runs from 6 to 7. Probably no one will cry, but you never know.)