PORTLAND, Ore. (AP) — The party at the Salmon Street Springs fountain, a riverfront landmark in the heart of Portland, was just getting started.

Dozens of drummers beat out entrancing rhythms and a crowd of hundreds danced joyfully and wildly. Poster boards bore the names of dozens of Black men and women killed by police, and 10-year-old Xavier Minor jumped into the center of the circle and started dancing with abandon. The emcee took note.

“Yo, Black kids are the future! Black kids are the future!” he shouted.

A few minutes later, as night fell, the music stopped — and the march to the federal courthouse began.

Two blocks away, the several dozen federal law enforcement agents guarding the Mark O. Hatfield Federal Courthouse could hear the crowd of protesters — about 4,000 people at its peak.

“It’s scary. You open those doors out, when the crowd is shaking the fence, and ... on the other side of that fence are people that want to kill you because of the job we chose to do and what we represent,” said a Deputy U.S. Marshal who has been protecting the courthouse for weeks. He requested anonymity because protesters identified him previously and posted personal information about him online.

"I am worried for my life, every time I walk outside of the building,” he said.

This weekend, journalists for the Associated Press were both outside, with the protesters, and inside the courthouse, with the federal agents, documenting the chaotic fight that has become an unlikely centerpiece of the protest movement gripping America.

It started with dancing but quickly turned violent.

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Small pods of three to four protesters dressed in black circulated in the crowd, stopping every few minutes to point green laser beams in the eyes of agents posted as lookouts on porticoes on the courthouse's upper stories. The agents above were silhouetted against the dark sky as dozens of green dots from the lasers and a large spotlight played on the courthouse walls, projected from somewhere in the back of the crowd.

Someone in the crowd fired a commercial-grade firework inside the fence. Next came a flare and then protesters began using an angle grinder to eat away at the fence. A barrage of items came whizzing into the courthouse: rocks, cans of beans, water bottles, potatoes and rubber bouncy balls that cause the agents to slip and fall.

Federal agents at the fence perimeter fired the first tear gas of the night.

Inside the courthouse, agents on scaffolding fired pepper balls through the window slits at the crowd while others sat quietly on marble benches in the lobby, alone or in small groups, and waited for their turn at the fence.

The Federal Protective Service and U.S. Marshals Service agents, dozens of whom live in the Portland area themselves, were tired and frustrated. They didn't want to confront the crowd; they just wanted to go home. Many were sent in from out of town to reinforce the agents - some are members of an elite Border Patrol tactical team sent in as reinforcements. But others were already stationed there and said they had chosen to live in the Portland area and call it home.

“My friends have been hit in the head with hammers. I know people who have been shot with fireworks. It’s disgusting,” said the Deputy U.S. Marshal who’s been at the courthouse for weeks. “I’ve never thought I’d have to walk around in my office building wearing a gas mask to go sit in front of my computer.”

Outside, the vapors, indiscriminate, hit a man biking past, a middle school teacher, a musician, a volunteer medic and dozens of others who'd been far back in the protest crowd dancing to the drums and chanting.

“I think what people fail to realize is, us in Portland, we’re still playing defense so anything we do, it’s a defensive maneuver. We are protecting ourselves at the very most and each other,” said Eli Deschera, 21.

“I think that using chemical warfare on civilians is anything but protecting and serving, which is what they’re supposed to be doing," said Deschera, of Portland.

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By 2:30 a.m., the protest was down to a few hundred people. Tear gas canisters bounced and rolled in the street, their payload fizzing out into the air before protesters picked them up and hurled them back over the fence at the agents, who held their ground quietly.

Finally, a line of agents marched in lock step down Third Street, pushing the crowd in front of them with tear gas and pepper balls. People scattered and small groups roamed the downtown as tear gas choked the air.

In less than two hours, it would be daylight.

The battle over, the agents and the demonstrators gathered their things and left to get some sleep, protesters and protectors sleeping in the same city — perhaps even on the same street — resting up for the next night's fight.

For at nightfall, it will all begin again.

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Balsamo reported from inside the courthouse with the federal agents; Flaccus reported from outside with the protesters. Associated Press writer Sara Cline in Salem, Oregon; Associated Press photographers Noah Berger and Marcio Sanchez in Portland, Oregon; and Associated Press video journalist Aron Ranen in Portland, Oregon all contributed to this report.

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Follow Gillian Flaccus on Twitter at @gflaccus and Mike Balsamo at @MikeBalsamo1.

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