Former President Donald Trump on Saturday repeatedly swerved from a message focused on the economy into non-sequiturs and personal attacks, including declaring several times that he was better looking than Vice President Kamala Harris.

Trump wound back and forth between hitting his points on economic policy and delivering a smattering of insults and impressions of President Biden and French President Emmanuel Macron as he held a rally in northeastern Pennsylvania.

The former president has seemed to struggle to adjust to his new opponent after Democrats replaced their nominee. Over the past week, he has diverged during campaign appearances away from the policies he was billed to speak about and instead diverted to a rotation of insults.

Trump seemed to spend more of his rally on Saturday than usual sticking to the script, but he diverged early and often.

As he attacked Democrats for inflation at the top of his speech, he asked his crowd of supporters, “You don’t mind if I go off teleprompter for a second, do you? Joe Biden hates her.”

Trump’s rally was in a swath of the pivotal battleground state where he hopes conservative, white working-class voters near Mr. Biden’s hometown will boost the Republican’s chances of winning back the White House.

His remarks Saturday came as Democrats prepare for their four-day national convention that kicks off Monday in Chicago and will mark the party’s welcoming of Harris as their nominee. Her replacement of Mr. Biden less than four months before the November election reinvigorated Democrats and their coalition and has presented a new challenge for Trump.

Trump on Saturday hammered Harris on the economy, associating her with the Biden administration’s inflation woes and likening her latest proposal against price gouging to measures in communist nations. Trump has said a federal ban on price gouging for groceries would lead to food shortages, rationing and hunger and on Saturday asked why she hadn’t worked to solve prices when she and Mr. Biden were sworn into office in 2021.

“Day one for Kamala was three and a half years ago. So why didn’t she do it then? So this is day 1,305,” Trump said.

To address high prices, Trump said he would sign an executive order on his first day sworn in as president “directing every cabinet secretary and agency head to use every power we have to drive prices down, but we’re going to drive them down in a capitalist way, not in a communist way,” he said.

But he maundered in his remarks, touching on the chaotic withdrawal from Afghanistan in 2021 to doing impressions of Macron’s French accent. But he took issue with the way his free-wheeling style is typically portrayed in news reports.

“They will say he’s rambling. I don’t ramble. I’m a really smart guy. I don’t ramble.”

Trump laced in attacks on Harris’ laugh and said she was “not a very good wordsmith” and mocked the names of the CNN anchors who moderated the debate he had with Mr. Biden in June.

When he began musing on Harris’ recent image on the cover of Time magazine, he forked off, commenting on the picture’s resemblance to classic Hollywood icons Sophia Loren and Elizabeth Taylor and then took issue with a Wall Street Journal columnist remarking earlier this month on Harris’ beauty.

“I am much better looking than her,” Trump said, drawing laughs from the crowd. “I’m a better looking person than Kamala.”

He predicted financial ruin for the country and Pennsylvania in particular if Harris wins, citing her past opposition to fracking, an oil and gas extraction process.

“Your state’s going to be ruined anyway. She’s totally anti-fracking,” Trump said.

In 2016 and 2020, Trump crushed his Democratic rivals in the county that is home to blue-collar Wilkes-Barre. The Rust Belt region, home to Mr. Biden’s native Scranton, offers Trump hope and helps him spotlight Democratic vulnerabilities after the president ended his reelection bid and Harris launched her campaign.

Her campaign has tried to soften her stance on fracking, saying she would not ban it, even though that was her position when she was seeking the 2020 presidential nomination.

Some Democrats in Pennsylvania acknowledge the challenges but say the economy is what concerns most people in the area.

On Sunday, Harris plans a bus tour starting in Pittsburgh, with a stop in Rochester, a small town to the north. Trump has scheduled a visit Monday to a plant that manufactures nuclear fuel containers in York. Trump’s running mate JD Vance is expected to be in Philadelphia that day.

Trump’s Saturday rally was his fifth at the arena in Wilkes-Barre, the largest city in Luzerne County, where he has had victories the past two elections. Mr. Biden bested Trump in neighboring Lackawanna County, where the Democrat has long promoted his working-class roots in Scranton.

Some of Mr. Biden’s loyal supporters in this former industrial city of 76,000 were upset to see party leaders put pressure the president to step aside.

Diane Munley, 63, says she called dozens of members of Congress to vouch for Mr. Biden. Munley eventually came to terms with Mr. Biden’s decision and is now very supportive of Harris.

“I can’t deny the enthusiasm that’s been going on with this ticket right now. I am so into it,” Munley said. “It just wasn’t happening with Joe, and I couldn’t see it at the time because I was so connected to him.”

Robert A. Bridy, 64, a laborer from Shamokin, Pennsylvania, traveled on Saturday to the rally to show support for Trump. He said the election feels tight in this state and added that his union and a close friend are trying to convince him to vote for Harris and other Democrats, but he has voted for Trump since 2016.

Bridy called Trump a “working class guy like us.” Trump is a billionaire who built his fortune in real estate.

“He’s a fighter,” Bridy said. “I’d like to see the closed borders. He doesn’t mess around. He goes at it right away and takes care of business the way it should be.”