Judge Merchan read the jury the New York state law related to falsifying business records.

"Under our law, a person is guilty of falsifying business records in the first degree when, with intent to defraud that includes an intent to commit another crime or to aid or conceal the commission thereof," Merchan read.

Few of the jurors appeared to be taking the notes at that point.

Judge Merchan then reviewed each of the counts against Trump to explain the People's burden of proof.

He said that in the interest of brevity, he would instruct them on Falsification of Business Records for the first count -- but not the full instruction for all 34 counts, because they are identical.

Merchan methodically walked through each of the allegedly falsified documents, listing the dates, voucher numbers, and check numbers for each of the records.

The judge said he would be happy to repeat the instructions later if the jury so requests.

Judge Merchan explained to jurors the prosecution's three theories for the unlawful means used to influence the 2016 election.

First, Merchan said that the unlawful means could include a violation of the Federal Election Campaign Act, which caps campaign contributions. Prosecutors allege that Michael Cohen's payment to Stormy Daniels exceeded the legal cap.

Second, Merchan said prosecutors argue that Trump and others falsified business records, including the bank paperwork for Essential Consultants Inc., the money wire to Daniels, and the 1099 forms related to Cohen's repayment.

Third, Merchan said the crime could be violations of tax laws related to the "grossing up" of Cohen's reimbursement to cover the taxes he would owe on the payment.

Judge Merchan tells the jury that prosecutors allege that Trump attempted to conceal a violation of New York election law by falsifying business records.

"They need not prove that the other crime was committed, aided, or concealed," Merchan said.

Prosecutors are relying on New York Election Law 17-152, which prohibits "any two or more persons who conspire to promote or prevent the election of any person to a public office by unlawful means." Prosecutors offered three theories of the "unlawful means" mentioned in that law.

Though jurors will need to agree Trump falsified records in furtherance of an additional crime in order to convict, "they need not be unanimous" on "what unlawful means" were used, Merchan said.

As ABC News reported previously, the U.S. Secret Service spent considerable time working with New York City court and jail officials to determine what would happen if the judge, as threatened during trial, ordered former President Trump to be incarcerated for contempt -- a situation that did not come to pass.

According to an official briefed on the matter, U.S. Secret Service planners have not started the process of determining arrangements for Trump to be imprisoned at a New York state penitentiary in the event he is convicted. Because Trump is charged with nonviolent crimes, has no criminal record, and was allowed to remain free before trial, it is believed that there is no way that a conviction would lead to immediate incarceration.

If Trump is convicted, the Secret Service will spend the time prior to sentencing -- which could be months -- working with New York state prison officials to determine how imprisonment would work. An official told ABC News that potential questions could include, would USSS agents be armed inside prisons where firearms are prohibited? What prison would Trump be assigned to? Where would protection agents be stationed in relation to Trump? Those details, among many others, would have to be hammered out, the official said.

The Secret Service specifically avoided planning on a possible prison sentence during the trial so Trump and his loyalists could not accuse them of taking sides against the former president, the official said.

-Josh Margolin