The cheers followed them down East Capitol Street, then around the corner toward the court. The Tennessee plaintiffs walked between long separated lines of spectators, drawing kisses and applause from the staid, suited lawyers’ line and shouts of “Give ’em hell!” from the scruffier line for the public.

“We’re Tennessee!” shouted Abby Rubenfeld, one of their attorneys. She held up her hand for high-fives, like a basketball player coming in for warm-ups. “We’re gonna win!”

On Tuesday morning, in the hours before the Supreme Court heard a landmark case that could legalize same-sex marriage nationwide, the mood outside the court was expectant and jubilant at once. Encouraged by past rulings, many supporters of same-sex marriage were confident that their side would win.

“I just think the time is right. The law is right, and the Supreme Court is giving all the signs,” Rubenfeld said in an interview. The day’s cases involved plaintiffs from four states: Tennessee, Kentucky, Michigan and Ohio. “The court wants us to win.”

Social video captures the scene outside the Supreme Court as justices weigh same-sex-marriage arguments. (The Washington Post)

That mood carried through the day as hundreds — mainly supporters of same-sex marriage — crowded the sidewalk outside the court. Their cause has advanced so fast that, in this case, it seemed as if it had outrun history itself: People were so sure the court will rule their way in June that they were celebrating now.

Even before the justices had heard the first word of argument.

“It’s a celebration. It feels like a rally. It feels like a Pride [Day], and in a lot of ways it is,” said Callie McLoughlin-McKee, 36, who had come from Ann Arbor, Mich.

Around her, couples carried signs with the number of years they had been together. The Gay Men’s Chorus sang “We Shall Overcome.” Several people brought their dogs. There were costumes: men in nuns’ habits, a man in a tutu, a girl in a unicorn mask. It was the kind of event where even the Westboro Baptist Church could be happily mocked.

“Let it go! Let it goooooo! Kick ’em out and slam the door!” sang Shirley Phelps-Roper, a leader of the famously anti-gay church. She was singing an alternative version of the song “Let It Go” from the movie “Frozen,” while holding four anti-gay signs at once.

McLoughlin-McKee was nearby. She works in theater. She could not stand by and do nothing. “I don’t think they should be able to take Disney from us,” she said. “They can’t take musicals from the gays. That’s just over the line.”

So she jumped in and belted out the original Disney lyrics, trying to drown out the Westboro version. “Not on my bucket list,” she said afterward.

The crowd also included smaller but vocal groups of people opposed to same-sex marriage. Some were well organized. The Alliance Defending Freedom showed up early with a small podium, ponchos, doughnuts, a pallet of bottled water, Band-Aids, avocados, knives for cutting avocados, sweatshirts, blankets and tarps. They wanted to have enough stuff to share, one staffer said, even with their opponents. (“We’re not really enemies,” she said. “We’re just on different sides.”)

That group’s speakers focused on state’s rights, saying that the definition of marriage should be left to voters, state by state. “The nine unelected justices aren’t the Supreme Policymakers,” said Caleb Dalton, one of the group’s lawyers.

In other places outside the court, Orthodox Jews and Christian groups shouted biblical condemnations. But even among those groups there was some pessimism about their chances in court.

“Oh, extremely small,” said Buddy Fisher, a salesman from North Carolina and the leader of a Christian group called Itching Ears Ministry. “With God, all things are possible. But no, this battle was lost in America when the 26th state accepted same-sex marriage.”

Some people, on both sides, had already spent days outside the court, staking out a spot on the sidewalk or in a line.

Rabbis from New York and New Jersey demonstrate in front of the Supreme Court. (Allison Shelley/For The Washington Post)

“Ever since I was a little boy, I just wanted to see Mary Bonauto argue this case,” said Sean Varsho, a law student who had come from Chicago and spent four days in front of the court with the District’s professional line-standers. Varsho sneaked away to Starbucks at 5 a.m. to put on a suit to see Bonauto, a legendary lawyer involved in a number of gay rights cases. He was sure she will win. “One hundred percent,” Varsho said.

“It’s just like, you know, this special piece of history that nobody else has,” Varsho said, meaning the moment in the courtroom, where no cameras are allowed. When they win, he added, he’ll be able say, “I was there.”

People hold signs in front of the Supreme Court on Tuesday; see more at washingtonpost on Snapchat. (Julia Carpenter/The Washington Post)

On the court sidewalk, the two camps mostly talked past each other — the hope of saving a soul was dim on both sides. When people began filing into the court, for instance, Fisher’s group of Christians began shouting insults at them through a bullhorn. The spectators, heading in, turned their cellphone cameras toward the court. They controlled the video of this moment, if not the audio.

The last to go in were spectators in the “three-minute line,” who would wait to be allowed to watch the arguments for just three minutes. One of them was Rio Franciosa, 26, a student from New Jersey who had come with his boyfriend. While he waited, he walked up to taunt the taunters.

“How many of you smoke marijuana?” yelled Jesse Morrell, clutching a bullhorn.

“Yeah!” Franciosa yelled.

“How many of you think it’s okay to be gay?”

“Yeah!” Franciosa yelled. “Gay marijuana for all!”

They argued more, about who in the crowd deserved God’s love.

“You’re a false prophet!” Morrell shouted back.

“I’m a prophet!” Franciosa yelled back, delighted at the promotion. He went back to the three-minute line.

“That three minutes is going to be the best three minutes of my life,” he said.

Later in the day, when the arguments were over, the crowds turned to watch the court, waiting for the plaintiffs and their attorneys to emerge.

“Love must win!” the pro-same-sex-marriage crowd chanted.

“Don’t end debate!” the opponents chanted back.

Finally, the plaintiffs emerged, celebrities for the day, and held a news conference. “What would be the impact if the ruling went against you?” a reporter asked.

It was the question nobody in the happy crowd had wanted to contemplate. At the back of the crowd of plaintiffs, 73-year-old Luke Barlow spoke up. He was one of the Kentucky plaintiffs, who has been with his husband for 47 years and now wants his out-of-state marriage recognized in his home state.

“Don’t ask me that!” he said.

Outside the court on Tuesday. (Mladen Antonov/AFP/Getty Images)