Former U.S. president Donald Trump will hold a rally in Harrisburg, Pa., on Wednesday evening, returning to the stage in the same battleground state where a gunman tried to kill him earlier this month.

Trump's event is being held indoors at the state capital's New Holland Arena. It is due to get underway at 6 p.m. ET, according to his campaign website.

Thousands of people were lined up outside the venue in temperatures upward of 30 C for hours before the arena doors opened mid-afternoon. Many wore T-shirts and other merchandise with a photo of Trump, 78, raising his fist in the air after the shooting at his last Pennsylvania rally on July 13.

"It's amazing [Trump's] here," said Xena Colasante, 35, who drove to the rally with her husband from their home in West Grove, about 100 kilometres southeast of Harrisburg.

"That's why we wanted to make sure we show a really good show of support for him, since he's brave enough to come back."

Trump was on stage in Butler, Pa., when a gunman fired at him from the roof of a nearby warehouse. Trump's right ear was wounded, a rally attendee was killed and two more were hurt.

The gunman was shot dead at the scene. 

Wednesday's indoor rally marks a change from previous Trump campaign events, which have largely been held outside. There was heavy police presence outside the building.

Pennsylvania will be a critical battleground state when Americans vote in November. Trump won the state back from the Democrats in 2016, only to lose is again to U.S. President Joe Biden four years later.

Rallygoers who spoke with CBC News said inflation, immigration and the wars involving Russia, Ukraine, Israel and Gaza were their main concerns heading into the election. Several said they could look past Trump's character because they prefer his policies on those portfolios.

"I think he's the right guy for the job. We know he's not perfect. We've all come short, glory of God, but he appears to be the best guy for the job right now," said Ross Willard, 73, who lives roughly two kilometres away from the arena and went to the event with his wife and their 10-year-old granddaughter.

Changes in presidential race

The director of the U.S. Secret Service stepped down over security failures leading up to the attempt on Trump's life in Butler, telling a congressional committee it had been the agency's most serious operational failure in decades.

The FBI is still investigating the shooting, as are a bipartisan task force in Washington and other U.S. authorities.

Since the attempt on Trump's life, there have been several dramatic developments in the U.S. presidential campaign.

On July 21, Biden withdrew from his re-election bid, endorsing Vice-President Kamala Harris to take his place at the top of the ticket for the Democrats.

Harris has since secured the support of enough Democrat delegates to become the party's likely presidential nominee.

A Harris-Trump matchup gives U.S. voters a change from the previous election in 2020, in which Biden faced off against Trump.

Harris has not yet picked a running mate. Trump, meanwhile, has selected Ohio Sen. J.D. Vance to run alongside him.