Two days before his first criminal trial was set to begin in Manhattan, former President Donald J. Trump on Saturday again framed the charges he faces as a broad attempt by Democrats to keep him from the White House, and he criticized a gag order placed on him by the judge in the New York case.

“Two days from now, the entire world will witness the commencement of the very first Biden trial,” Mr. Trump said at a rally in eastern Pennsylvania, alluding to his frequent and false assertion that President Biden orchestrated the New York case.

The case, which Mr. Trump also called a “communist show trial,” was brought by the Manhattan district attorney’s office and has nothing to do with Mr. Biden.

As he often does, Mr. Trump, the presumptive Republican presidential nominee, cast himself as a victim of political persecution who is protecting his followers from a similar fate.

“I’m proud to do it for you,” he said of going on trial, speaking to a large crowd of his supporters who had waited for hours before gathering in a windswept field in Schnecksville, Pa. “Have a good time watching.”

There will not be television cameras in the courtroom. But Mr. Trump has sometimes held news conferences after his court dates, using them as an extension of the campaign trail, and he is expected to continue holding rallies on weekends, as he has for months.

Mr. Trump’s rally on Saturday began as Iran was launching an aerial attack on Israel in retaliation for a deadly Israeli airstrike two weeks ago.

The former president, who often portrays himself as Israel’s staunchest ally, offered prayers and support for the country. Then, as he often does, Mr. Trump effectively blamed Mr. Biden for the conflict in Gaza and insisted it would not have happened if he had won in 2020.

“They’re under attack right now,” Mr. Trump said of Israel. “That’s because we show great weakness.”

Several minutes later, members of the crowd began chanting, “Genocide Joe,” a phrase more commonly associated with progressives protesting Mr. Biden’s support for Israel’s war in Gaza.

Mr. Trump has repeatedly said that he backed Israel’s right to defend itself after a Hamas-led attack on Oct. 7. But, as the chants died down, he seemed to agree with them. “They’re not wrong,” he said.

Mr. Trump repeated his false claims that he won the 2020 election and that Democrats cheated him out of a victory several times. Mr. Biden won Pennsylvania in 2020 by more than 80,000 votes.

“They cheat like hell,” Mr. Trump said of his political opponents, an allegation of voter fraud that has not been supported by evidence. He continued by sowing doubts about the integrity of the election in November, telling his supporters: “When you see them cheating, you get out there and start screaming. Start screaming.”

Mr. Trump also criticized a gag order imposed on him in the Manhattan case, in which he has been accused of covering up a sex scandal surrounding the 2016 campaign.

That order prevents Mr. Trump from publicly attacking witnesses, jurors, court staff and prosecutors, though not the judge or Manhattan’s district attorney.

“I will be forced to sit fully gagged. I’m not allowed to talk,” Mr. Trump said. “Can you believe it? They want to take away my constitutional right to talk.”