TULSA, Okla. - Six members of the advance team preparing to staff President Trump's rally here Saturday tested positive for the coronavirus, underscoring concerns about holding a massive indoor event in a city where cases are spiking.

The campaign made that announcement, saying quarantine procedures had gone into effect for the infected staff members and those in "immediate contact" with them, as hundreds of supporters filled downtown streets in anticipation of the president's rally - his first since the virus brought much of public life to a standstill in March.

Upon entering the rally grounds, attendees were handed blue face coverings and directed through a maze of metal fencing, which led to a touchless temperature screening conducted by volunteers in purple smocks.

City police erected black fencing and other barriers around the 19,000-seat BOK Center, a private venue leased by the Trump campaign. Shortly before noon, the campaign directed officers to arrest a protester who had sat down within the barricaded zone, according to the police department.

The protester, Sheila Buck of Tulsa, said she had a ticket to the event. She was wearing a shirt that read, "I can't breathe," among the final words uttered by George Floyd as a police officer in Minneapolis knelt on his neck.

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Adding to the fortified atmosphere, about 250 National Guard soldiers were on hand to supplement local authorities. Some were armed after the threat level was elevated, said Lt. Col. Geoff Legler, a spokesman for the Guard. Initially, the plan was to equip them only with batons, shields and pepper spray.

The president is heading to Tulsa at a precarious moment for his presidency. Recent polls show him trailing former vice president Joe Biden nationally and in a number of critical swing states, suggesting he has suffered politically from his handling of the coronavirus - which has killed more than 120,000 Americans - and his response to roiling demonstrations over racial injustice and police brutality triggered by Floyd's killing last month.

The protests and the pandemic collided with Trump's visit to Tulsa, where the number of new coronavirus cases continues to mount. The county reported 136 new cases on Saturday - marking another high for both single-day and average cases - while the state as a whole reported 331 new infections.

Most police officers, National Guard soldiers, food vendors and the vast majority of people in line chose not to wear face coverings, though Trump-branded masks dotted the crowd. The Confederate flag also appeared - all the more striking because Oklahoma was not a state at the time of the Civil War.

Margene Dunivant and her son Christian Lynch, both of Tulsa, sat on the edge of the crowd, taking in the scene.

"Everybody here is just full-on American and American Dream and hard-working, and just believes in everything America," said Dunivant, 52. "Nowadays, it's like you put on a Trump shirt and you're considered racist, and it's just wrong. We're good people, and we love everybody."

A clashing view was also on display in Tulsa, where counteractions were planned with such names as "Dump the Trump Rally" and "Rally Against Hate." Antipathy to the president - and objections to his insistence on gathering thousands of people indoors for a campaign event - fused with the outpouring for Juneteenth, the holiday celebrating freedom for enslaved black people.

"It's irresponsible to say the least," said Mareo Johnson, a pastor and the founder of Black Lives Matter Tulsa. His organization was involved in organizing a Saturday demonstration at John Hope Franklin Reconciliation Park, less than a mile from the president's rally.

His message to the city's black residents, he said, was, "Stay focused on what Juneteenth represents."

The commemoration held added significance in Tulsa, a city scarred by racist violence in 1921, when a white mob killed an estimated 300 black residents and devastated an area of the city known at the time as "Black Wall Street." The Tulsa Race Massacre unfolded in the Greenwood neighborhood, where the words "Black Lives Matter" were painted on a road in bright yellow paint on Friday.

The events - freighted with political and historical meaning - turned the city into a magnet, leaving epidemiologists and public health officials fearful about the spread of the virus.

Susan Schoonover and her husband Brian said they woke up at 3 a.m. to drive the 15 miles from their home in Glenpool, Okla. Standing in line to see Trump, Schoonover sparkled in a tutu, tube socks and a red, white and blue head piece, clad for her first Trump rally. The pair purchased a cardboard cutout of Trump from Amazon to display in line, and they said it has been a hit with other attendees.

The parents of four left their children at home "just in case," they said, citing recent unrest in cities across the country. As for the pandemic, they did not discount the threat of the coronavirus and planned to take some precautions. If they were to contract the virus, however, "it's not a death sentence," they said, because both are in their early 30s. Older people with underlying medical conditions are especially vulnerable, but young adults have also been badly sickened, including by an inflammatory syndrome linked to covid-19, the disease caused by the coronavirus.

Robin Wilson, 64, said she was not concerned about contracting the virus inside the stadium despite a heart condition that put her in a wheelchair two years ago.

"I'm here because I love my president," said Wilson, who used to work in insurance, "and I feel that he's misrepresented by the mainstream media. And I believe that this is history in the making today, and I wanted to be a part of it."

Brian Clothier, 61, found a more eye-catching way to illustrate his view of possible risks from the coronavirus. He wore an adult diaper over his pants, where he placed a sign saying the underwear would "stop the spread," in a reference to the disputed notion that flatulence can be linked to coronavirus transmission.

By early Saturday, lines had formed around three major entrances to the arena, and state troopers and tactical teams in military-style fatigues were massing at the conference center across the street on the southwestern side of the downtown stadium.

The event was able to proceed after the Oklahoma Supreme Court on Friday rejected a bid to require the BOK Center to enforce social distancing guidelines spelled out by the Centers for Disease Control and Prevention and endorsed by members of the president's own coronavirus task force. The campaign said it would hand out masks but not require them.

The Trump campaign had originally scheduled the rally for Friday, Juneteenth, but postponed a day following an outcry. The president, after admitting not to have known about the significance of June 19 for many African Americans, claimed in an interview with the Wall Street Journal to have made it "famous." Some feared the one-day delay would not prevent conflict.

"My fear is that we will see Charlottesville 2.0 in Tulsa," said Karlos Hill, chair of the African and African American studies department at the University of Oklahoma, referring to the deadly "Unite the Right" rally in 2017.

In addition to crowds gathered for the rally and Juneteenth activities, an estimated 4,500 people were expected at an exposition space across town for the Oklahoma Gun Show and the Spring Home and Outdoor Living Expo. Discover Tulsa advertised the chance to see more than "70,000 square feet of guns this weekend."

Trump on Friday threatened protesters preparing to greet him in Tulsa, warning on Twitter: "Any protesters, anarchists, agitators, looters or lowlifes who are going to Oklahoma, please understand, you will not be treated like you have been in New York, Seattle or Minneapolis. It will be a much different scene!"

The Trump campaign has repeatedly touted figures suggesting as many as 1 million people have signed up for the event, vastly outstripping the arena's capacity.

A curfew that had been in place Thursday was rescinded for Friday night after discussions between Trump and Tulsa Mayor G.T. Bynum, a Republican, who has called the president's decision to hold the event in his city a "tremendous honor" while declining to attend it. The state's Republican governor, Kevin Stitt, has embraced the president's move, saying of concerns about the coronavirus, "We've got to learn to deal with this," while his health commissioner warned in a statement this week that "individuals looking to attend Saturday's event, or any other large-scale gathering, will face an increased risk of becoming infected with covid-19 and becoming a transmitter of this novel virus."

Though there was no curfew in place Friday, a "secure zone" was established around the site of the rally to "keep the area clear of individuals that are only present to break the law and disrupt the rights of people assembling peacefully," according to the Tulsa Police Department.

Andrea Anderson, an FBI spokeswoman in Oklahoma City, said the Bureau was supplying investigative resources to state and local partners to "ensure public safety and security."

This article was written by Robert Klemko, Arelis R. Hernández and Isaac Stanley-Becker, reporters for The Washington Post.