Former President Donald J. Trump lashed out at Republicans in Congress while campaigning in Pennsylvania on Saturday, threatening members of his party who do not share his appetite for pursuing corruption investigations against President Biden and his family — and for retribution.

In a litany of grievances about his deepening legal woes and the direction of the country, the twice-indicted former president cast G.O.P. holdouts as meek during a rally in Erie, Pa., criticizing their response to what he described as politically motivated prosecutions against him.

“The Republicans are very high class,” he said. “You’ve got to get a little bit lower class.”

And then Mr. Trump, the overwhelming front-runner for the 2024 Republican presidential nomination, put party members on notice.

“Any Republican that doesn’t act on Democratic fraud should be immediately primaried,” said Mr. Trump, to the roaring approval of several thousand supporters at the Erie Insurance Arena. Throughout the night he referenced the case against Hunter Biden and accused the president of complicity in his son’s troubles.

It was the first solo campaign event and the second public appearance for Mr. Trump since the Justice Department added charges against him in connection with his mishandling of classified documents after leaving office.

In a superseding indictment filed on Thursday in U.S. District Court in Florida, federal prosecutors presented evidence that Mr. Trump told the property manager of Mar-a-Lago, his private club and residence in Florida, that he wanted security camera footage there to be deleted.

Prosecutors also charged him, along with one of his personal aides, with conspiring to obstruct the government’s repeated attempts to reclaim the classified material.

On the same day that the additional charges were announced, Mr. Trump’s lawyers met with federal prosecutors to discuss another expected indictment, one centering on Mr. Trump’s efforts to overturn the 2020 election and his actions during the Jan. 6, 2021, attack on the U.S. Capitol.

To Mr. Trump’s unflinching supporters gathered inside the arena, the cascade of indictments was a punchline — if not a badge of honor.

Edward X. Young, 63, a debt consolidation company consultant and part-time actor who was dressed like Elvis Presley, wore a T-shirt with a mock-up mug shot of Mr. Trump. He said he had driven 10 hours from Point Pleasant, N.J., to attend Mr. Trump’s rally, his 59th.

“I think he’s being persecuted,” he said of the former president.

Ruth Jenkins, 61, a Republican from Rochester, N.Y., who works for a Wegmans grocery store, said that she did not believe that Mr. Trump had been motivated to run for president to avoid criminal liability.

“Well, who wouldn’t want to be kept out of prison?” she said, claiming that the latest charges against Mr. Trump were the latest attempt to shift attention away from the case against the president’s son.

As Mr. Trump prepared to take the stage, campaign workers helped fill in an empty section near the back of the arena, which had been configured to seat 8,000.

The playlist for the rally featured “Try That in a Small Town,” the Jason Aldean hit that was filmed at the site of a lynching and pulled from Country Music Television amid criticism.

With Mr. Trump as its standard-bearer, the Republican Party has watched Democrats in Pennsylvania secure high-profile victories in the last year, including flipping a U.S. Senate seat, holding on to the governor’s office and gaining control of the statehouse.

In 2020, Mr. Trump lost the battleground state by nearly 82,000 votes to Mr. Biden, who was born there.

Despite several courts rejecting his election lawsuits in Pennsylvania, Mr. Trump has continued to cling to falsehoods about results, including on Saturday.

“We got screwed,” he said, baselessly claiming that news outlets had delayed their race calls because he had been ahead. “I said, ‘Why aren’t they calling Pennsylvania?’”

Mr. Trump, who spoke for more than 100 minutes, said that he still had not decided whether he would take part in the first Republican presidential debate, which will take place on Aug. 23 and be televised by Fox News.

Mr. Trump said that there appeared to be little upside to debating on a “hostile” network — Fox News began to fall out of favor with the former president after it became the first major outlet to call Arizona for Mr. Biden in 2020 — and noted his commanding polling lead over his G.O.P. opponents. His nearest competitor, Gov. Ron DeSantis of Florida, trailed him by about 30 percentage points in national polls.

“If I don’t go to the debate, they say — I’m not saying this — they say the ratings are going to be very bad,” he said. “Should I do it or not?”

The crowd’s answer was resounding: “No.”