After the event, Mr. Biden, in response to a question from a reporter, again expressed regret for his 1998 use of the term “partisan lynching” in a discussion about impeachment proceedings against President Bill Clinton. Mr. Biden had also tweeted an apology on Tuesday for using the term.

“I was wrong to have said it and I apologize for having said it,” Mr. Biden said on Wednesday.

But he also criticized Mr. Trump for using the term “lynching,” with its legacy of racist murders of African-Americans, to describe the impeachment inquiry he currently faces. Mr. Trump, he argued, was using the term “as a dog whistle.”

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“When has he ever taken, when has he ever said a negative thing about a white supremacist?” Mr. Biden said of the president. “Have you heard him say anything? I haven’t.”

Mr. Biden’s appearance in Scranton came the same day that a new CNN national poll showed him with a commanding lead in the Democratic primary, with the support of 34 percent of Democrats and Democratic-leaning registered voters, followed by Ms. Warren at 19 percent and Senator Bernie Sanders at 16 percent. It is Mr. Biden’s widest lead in the CNN survey since shortly after he announced his bid for president.

But there is no national primary, of course, and Mr. Biden’s advantage in the early-primary states Iowa and New Hampshire has ebbed or evaporated. The CNN survey is a sign that nationally he has retained strong support despite facing weeks of unproved attacks by Mr. Trump on him and his son Hunter over their activities in Ukraine, an issue driving the Democrats’ impeachment inquiry.

Mr. Biden’s economic prescriptions, less sweeping than those of other leading Democrats seeking the nomination, include a $15 federal minimum wage, tripling funding for schools with at-risk students, free community college and a plan for students to pay down their college debt by committing to community service.

Pennsylvania’s unemployment rate is only 3.9 percent, though it is 5.2 percent in Lackawanna County, where Scranton is. But a manufacturing downturn may be underway statewide, with 8,100 jobs lost this year so far, an issue that could cut into the president’s 2016 promises to restore industry in the Rust Belt.