Within about an hour, a Manhattan jury will begin a discussion of historic import: determining whether Donald J. Trump is guilty of 34 felonies.
But before the jurors begin to deliberate, the judge, Juan M. Merchan, will deliver legal instructions that will help guide the 12 New Yorkers who will hash out Mr. Trump’s fate.
Justice Merchan will describe the legal meaning of the word “intent” and the concept of the presumption of innocence. He will remind the jurors that they pledged to set any biases aside against the former president before they were sworn in, and that Mr. Trump’s decision not to testify cannot be held against him.
Then, according to a person with knowledge of the instructions that Justice Merchan plans to deliver, he will explain the 34 charges of falsifying business records that Mr. Trump faces. It will likely be the most important guidance that the judge offers during the trial. And it is no simple task.
In New York, falsifying records is a misdemeanor, unless the documents were faked to hide another crime. The other crime, prosecutors say, was Mr. Trump’s 2016 violation of state election law that prohibited conspiring to aid a political campaign using “unlawful means.”
Those means, prosecutors argue, could include any of a menu of other crimes. And so each individual false-records charge that Mr. Trump faces contains within it multiple possible crimes that jurors must strive to understand.
The moment that the jurors begin to deliberate will mark the first time that the complicated case will be assessed not by judges or a parade of commentators, but by everyday New Yorkers. The group may be aided by the two jurors who are also lawyers — though neither appears to have criminal experience, and one said during jury selection that he knew “virtually nothing about criminal law.”
Marc F. Scholl, who served nearly 40 years in the district attorney’s office, noted that jury instructions are often difficult to follow, particularly given that, in New York, jurors are barred from keeping a copy of the guidance as they deliberate. And he said that defendants are often charged with several different crimes, requiring even more elaborate instructions.
Still, Mr. Scholl said, one point of complexity stood out: “Usually you don’t have this layering of these other crimes,” he said.
Justice Merchan, according to the person with knowledge of his legal instructions, will proceed through each of the 34 charges count by count, explaining to jurors what each requires prosecutors to have proved.
The knotty legal instructions were the product of intense argument between the prosecution and the defense, culminating in a hearing last week in which each side sought to persuade the judge to make minor edits that could have had a major impact.
For example, during the hearing, the defense implored the judge to add the word “willfully” twice to a paragraph that describes for jurors one of the potential crimes from the menu of “unlawful means.” These are the secondary crimes Mr. Trump could have used to aid in the election conspiracy.
The judge agreed with the defense, and with those two small tweaks appeared to eliminate the possibility that jurors could have found one of the unlawful means to be a civil violation of that federal law, rather than a criminal one.
But the prosecution won several other important victories. The judge rejected the defense’s request that jurors be unanimous on which “unlawful means” Mr. Trump had used to aid his election win. That request would have made reaching a verdict far more difficult.
Mr. Trump’s lawyers argued that while such unanimity was not required by law, it was within Justice Merchan’s discretion to ask for it. But prosecutors fired back, arguing that the former president should be treated like any other defendant.
Justice Merchan agreed. “What you’re asking me to do is change the law, and I’m not going to do that,” he told Mr. Trump’s lawyers.
