With two days left in his third presidential campaign, former President Donald J. Trump told supporters at a Pennsylvania rally on Sunday that he “shouldn’t have left” the White House at the end of his term, escalated his unfounded claims of voter fraud and said “I don’t mind” if reporters are shot at.

With the remarks, Mr. Trump used the final days of his campaign to offer voters a stark reminder of the violence that came at the end of his term when, after weeks of his false claims that he had won an election he had lost, a mob of his supporters stormed the Capitol to try to prevent the certification of President Biden’s victory.

Mr. Trump has not committed to accepting the 2024 election results unless he believes they are fair, and he has repeatedly suggested in recent weeks that the only plausible explanation for him losing in 2024 would be if Democrats “cheat.”

On Sunday, at an airport in Lititz, Pa., Mr. Trump diverted from a closing argument about the stakes of the race with Vice President Kamala Harris and instead, his voice audibly hoarse and his speech sluggish, indulged in his personal grievances as he called the Democratic Party “demonic.”

Reflecting on the state of border security at the end of his tenure, Mr. Trump said he regretted ever leaving office.

“I shouldn’t have left, I mean, honestly,” Mr. Trump said, adding, “we did so well, we had such a great—” and then cut himself off. He then immediately noted “so now, every polling booth has hundreds of lawyers standing there.”

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