TULSA, Okla. — President Trump sought to jump-start his re-election campaign on Saturday amid scandals battering his standing in Washington, traveling to Tulsa for his first political rally in months — but one that appeared to be a letdown in attendance while also a health risk given the surge in coronavirus cases in the state.

While the president’s campaign had claimed that more than a million people had sought tickets to attend the rally, the 19,000-seat BOK Center was still half empty by the time Mr. Trump landed in Tulsa. A second, outdoor venue where Mr. Trump was set to declare a “great American comeback” was so sparsely attended that he and Vice President Mike Pence both canceled appearances there.

Tim Murtaugh, a spokesman for the Trump campaign, falsely blamed the small numbers on “radical protesters” and the news media who he said frightened away supporters. But there were few protests in the area, a strong security presence and no one blocking entrances.

The weak turnout came as Mr. Trump already found himself under siege about his sudden firing of the U.S. attorney in Manhattan and his losing legal battle over the release of a memoir full of damaging revelations by John R. Bolton, his former national security adviser. And in Tulsa, Mr. Trump faced criticism for ignoring pleas from officials about health risks to rallygoers and dismissing the grim symbolism of restarting his “Make America Great Again!” rallies in a city where a white mob massacred hundreds of black residents 99 years ago.

Many of the thousands of Trump supporters at the rally did not wear masks or stand six feet apart — health precautions that Mr. Trump himself has ignored. The campaign conducted temperature checks and handed out masks, yet health experts remained concerned that the event could be a dangerous incubator for the virus, spreading through the building’s recirculated air.

A few hours before the event, the campaign disclosed that six Trump campaign staff members who had been working on the rally had tested positive for the coronavirus during a routine screening. Two members of the Secret Service in Tulsa also tested positive for the virus, according to people familiar with the matter. Mr. Trump, who was made aware of the sick campaign aides before departing for the rally, was incensed that the news was made public, according to two people familiar with his reaction.

While rallies are Mr. Trump’s favorite events, election-year politics has changed since his last one, on March 2. The coronavirus has largely shut down the campaign trail, and more recently the national political conversation has been dominated by a fierce debate over police violence against black Americans after the killing of George Floyd in Minneapolis. Mr. Floyd’s death has sparked global protests against systemic racism and demands for police reform.

But the altered political landscape has had little effect on the president, whom advisers describe as feeling like a caged animal during the national lockdown that forced him to abandon most travel. They say he is determined to recapture the excitement of his pre-virus campaign rallies, but this one seemed unlikely to offer much relief to Mr. Trump.

He flew to Oklahoma amid mounting questions about the firing of Geoffrey S. Berman, the United States Attorney in Manhattan, whose office had investigated some of the president’s closest allies, imprisoning Michael Cohen, his former personal lawyer, and began an inquiry into Rudolph W. Giuliani, his current lawyer.

On Saturday morning, Attorney General William P. Barr announced that Mr. Trump had personally approved Mr. Berman’s firing. But only hours later, as Mr. Trump left the White House for the trip to Tulsa, the president said that “we have a very capable attorney general, so that’s really up to him. I’m not involved.”

The campaign had chosen to return first to Oklahoma, which the president won by 36 points in 2016, because they assumed he would be wildly popular there. Aides to Mr. Trump spent the week boasting about enormous interest from people in the rally, and Mr. Trump bragged on Saturday as he left for Oklahoma that ”the crowds are unbelievable” — a fiction that could raise questions about whether Trump rallies still have political potency.

Speaking at the rally before the president took the stage, Mr. Pence urged the crowd to bring the enthusiasm that helped sweep Mr. Trump into office in 2016. “Get ready. Buckle up,” he said. “It’s on. We’ve got a little more than four months to win four more years for President Donald Trump in the White House. So get ready to bring it.”

Many people in Tulsa, worried about the record numbers of coronavirus cases in Oklahoma in recent days, did not welcome the rally. On Saturday afternoon, local black leaders held a news conference in the city’s historic Greenwood neighborhood, where the 1921 massacre took place, pleading with the city’s mayor, G.T. Bynum, a Trump ally, to cancel the rally.

The community members, who included a range of religious leaders and civil rights activists, stood in front of the memorial dedicated to the victims of the massacre. Invoking the tragedy, they argued that the rally would wound a city that has worked hard at creating a shared language of racial reconciliation, and that black Tulsans could bear the brunt of any coronavirus surge.

“This is more about scoring political points with this president than the health of their citizens,” said Pastor Robert Turner of the historic Vernon A.M.E. Church on Greenwood Avenue, one of only structures still standing from 1921.

In the streets around the BOK Center, the president’s supporters — some of whom had lined up for days in the hopes of ensuring a seat in the stadium — gathered not far from Black Lives Matter protesters and people in town for the Juneteenth celebration. Many wore red MAGA hats while others wore caps with patriotic emblems or colors. Some waved red, white and blue banners with the Trump 2020 logo, the American flag, or the “Don’t Tread on Me” flag. Some wore them like capes. Almost none wore masks.

“If it is God’s will that I get coronavirus that is the will of the Almighty. I will not live in fear,” said Robert Montanelli, a resident of Broken Arrow, a Tulsa suburb.

The president and his advisers hope the return to campaign trail will help deflect attention from a daily stream of crises engulfing the White House. On Saturday, a federal judge refused to block the release of Mr. Bolton’s book, though he said the former national security aide may be personally liable for revealing classified information.

People close to Mr. Trump also said that the lack of regular adulation that he receives from the cheering crowds since the coronavirus lockdowns has left him morose and irritable. And his advisers hope that the rally will be an outlet for his energy, as opposed to his Twitter feed, where he has posted several self-destructive messages in the last several weeks.

Driven in part by poll numbers showing his support slipping as he prepares to face former Vice President Joseph R. Biden Jr. in the fall, Mr. Trump had initially scheduled his rally for Friday. He later said he was unaware of the significance of the Juneteenth holiday, which celebrates the end of slavery in the country.

Under fire, the campaign moved the event to Saturday, leaving Mr. Trump to make the wild claim that he had revealed the existence of the holiday to many people despite the fact that millions of black Americans have celebrated Juneteenth annually for years.

“I did something good: I made Juneteenth very famous,” Mr. Trump bragged in an interview with The Wall Street Journal. “It’s actually an important event, an important time. But nobody had ever heard of it.”

Local officials expressed anxiety about the possibility of clashes between supporters of Mr. Trump and protesters, a fear that was heightened when the president on Friday appeared to threaten the use of military force to quell any violence that might erupt during his visit. But the protests leading up to the rally were peaceful and relatively small.

Mr. Trump’s rally is taking place amid a spike of coronavirus cases in Oklahoma recently. The state reported its highest number of cases in a single day on Thursday, with more than 450 people testing positive for the virus, more than twice the average number of positive cases during the last several months.

Still, the Oklahoma Supreme Court ruled on Friday that Mr. Trump’s rally could move forward in its usual, boisterous manner, turning back a lawsuit by local business owners and others in Tulsa who had demanded that the president’s campaign adhere to social distancing rules or cancel the rally altogether.

Kayleigh McEnany, the White House press secretary, said Friday that the campaign will check temperatures at the entrance to the rally and distribute hand sanitizer and masks, though she made clear that Mr. Trump’s supporters will be under no obligation to wear the masks if they choose not to.

Mr. Trump has repeatedly refused to wear a mask and has suggested that people who wear them are doing so to spite him. Asked whether she would be wearing a mask at the rally, Ms. McEnany said she would not.

“It’s a personal decision. I’m tested regularly. I feel that it’s safe for me not to be wearing a mask, and I’m in compliance with C.D.C. guidelines, which are recommended, but not required,” she said. In fact, health experts — including the president’s own advisers — have urged people to wear masks, especially in indoor settings where social distancing is difficult.

By late morning in Tulsa on Saturday, a steadily growing line of rallygoers had assembled. Some had traveled significant distances, but many other attendees were Tulsa locals or came from nearby states, like Kansas and Missouri, or elsewhere in deep-red Oklahoma. The crowd was overwhelmingly white, and in more than a dozen interviews, most people ranged in age from their 40s to their 60s, though a sizable number of attendees also brought their children.

No one interviewed expressed serious concerns about coronavirus risk at the rally.

“It’s all fake,” said Mike Alcorn, 40, who works in maintenance and lives in Wichita, Kan. “They’re just making the numbers up. I haven’t seen anybody die, not from coronavirus. I don’t even know anybody who’s got it.”

Cynthia Bellino, who said she arrived at the rally site at 3 a.m. with her daughter, was there to support Mr. Trump in part out of appreciation for the anti-abortion measures he backs, an issue several attendees raised as they gathered in this conservative state. She was aware of his faltering poll numbers, but said she was tuning them out.

“The polls the first time were completely wrong,” she said. “I don’t pay them any attention.”

Ben Fenwick and Katie Glueck contributed reporting from Tulsa.