Facing a potential indictment, President Trump took a defiant stance at a rally Saturday in Waco, disparaging the prosecutors investigating him and predicting his vindication as he rallied supporters in a city made famous by deadly resistance against law enforcement.

With a hand over his heart, Mr. Trump stood at attention when his rally opened with a song called “Justice for All” performed by a choir of people imprisoned for their roles in the January 6 riot at the U.S. Capitol. Some footage from the day’s events was shown on big screens displayed at the rally site as the choir sang the national anthem and a recording played of Mr. Trump reciting the Pledge of Allegiance.

The extraordinary display opened Trump’s first rally of his 2024 Republican presidential campaign. He then launched into a speech brimming with resentments and framed the probes, including a New York grand jury investigation, as political attacks on him and his followers.

“You will be vindicated and proud,” Mr. Trump said “The thugs and criminals who are corrupting our justice system will be defeated, discredited and totally disgraced.”

Mr. Trump’s event at the airport grounds in Waco was part of a broader effort by the former president to use the potential indictment as a rallying cry for supporters to maintain his status as the GOP frontrunner in what is expected to be a crowded primary. It came one day after Mr. Trump raised the specter of violence should he become the first former president in U.S. history to face criminal charges.

Mr Trump declared his innocence in the Manhattan investigation into a hush money payment made during the 2016 election to porn actor Stormy Daniels to keep her from going public about a sexual encounter she said she had with Mr.. Trump years earlier. A grand jury hearing the case is expected to meet again on Monday.

Mr. Trump said the Manhattan district attorney was investigating him “for something that is not a crime, not a misdemeanor, not an affair.”

Some of Mr. Trump’s recent rhetoric, including at the rally, has echoed language he used before the Capitol insurrection by a mob of his supporters seeking to stop the transfer of power to President Biden, who won the election.

Mr. Trump declared Saturday that his “enemies are desperate to stop us” and that “our opponents have done everything they can to crush our spirit and to break our will.”

He added: “But they failed. They’ve only made us stronger. And 2024 is the final battle, it’s going to be the big one. You put me back in the White House, their reign will be over and America will be a free nation once again.”

Mr. Trump could be indicted soon by a Manhattan grand jury investigating a $130,000 payment that Trump’s longtime lawyer and fixer, Michael Cohen, made as Mr. Trump was in the throes of his 2016 presidential campaign.

Mr. Trump later reimbursed Cohen and his company logged the reimbursements as a legal expense. Cohen has already served time in prison after pleading guilty to campaign finance charges and lying to Congress, among other crimes.

Mr. Trump’s eyebrow-raising choice of venue in Waco for his first rally came amid the 30th anniversary of a 51-day standoff and deadly siege between U.S. law enforcement and the Branch Davidians that resulted in the deaths of more than 80 members of the religious cult and four federal agents and has become a touchstone for far-right extremists and militia groups.

Mr. Trump’s campaign insisted the location and timing of the event had nothing to do with the Waco siege or anniversary. A spokesperson said the site, 17 miles from the Branch Davidian compound, was chosen because it was conveniently situated near four of the state’s biggest metropolitan areas — Dallas/Fort Worth, Houston, Austin and San Antonio — and has the infrastructure to handle a sizable crowd.

Mr. Trump did not make any direct references in his speech to Waco’s history, telling the crowd of thousands that he wanted to hold his rally in a place with overwhelming support, not “one of those 50-50 areas.”

At several points, Trump criticized Florida’s Governor DeSantis, who is expected to run for president and is seen as his strongest potential challenger for the GOP nomination. Mr. Trump called his onetime ally disloyal and said he was “dropping like a rock.”

Audience members were holding red and white signs handed out by the campaign that said “Witch Hunt,” “Trump 2024” and “I stand with Trump.”

Hours before Mr. Trump arrived, hundreds of his supporters began streaming into the airport past vendors selling merchandise including Trump flags, bumper stickers and action figures.

Among them was Eugene Torres, 41, who said he was unfazed by the prospect that Trump could be indicted.

“It’s just another political attack on him to keep him from running and winning this race again,” said Mr. Torres, who is from the Texas coast city of Corpus Christi.

Alan Kregel, 56, traveled with his wife from Dallas to see Mr. Trump in person for the first time. While he voted for Mr. Trump in 2016 and 2020, he said he felt the former president’s “methods and vocabulary” often detracted from his policies. But now, two years out of office, he said he is more supportive of Trump than he was before.

“He’s an innocent man, just persecuted,” said Mr. Kregel, arguing an indictment would help Trump win in 2024.