NEW YORK — The judge in Donald Trump's hush money trial fined him $1,000 on Monday and, in his sternest warning yet, told the former president that future gag order violations could send him to jail. The reprimand opened a revelatory day of testimony, as jurors for the first time heard the details of the financial transactions at the center of the case and saw payment checks bearing Trump's signature.

The testimony from former Trump Organization controller Jeffrey McConney provided a mechanical but vital recitation of how the company reimbursed payments that were allegedly meant to suppress embarrassing stories from surfacing during Trump's 2016 presidential campaign and then logged them as legal expenses in a manner that Manhattan prosecutors say broke the law.

McConney's appearance on the witness stand came as the first criminal trial of a former U.S. president entered its third week of testimony. His account lacked the human drama offered Friday by longtime Trump aide Hope Hicks, but it nonetheless yielded an important building block for prosecutors trying to pull back the curtain on what they say was a corporate records cover-up of transactions designed to protect Trump's presidential bid during a pivotal stretch of the race.

At the center of the testimony was a $130,000 payment Trump's then-lawyer and fixer Michael Cohen made to porn actor Stormy Daniels in October 2016 to stifle her claims of an extramarital sexual encounter with Trump a decade earlier.

The 34 felony counts of falsifying business records accuse Trump of labeling the money paid to Cohen in his company's records as legal fees. Prosecutors contend that by paying him income and giving him extra to account for taxes in monthly installments for a year, the Trump executives were able to conceal the reimbursement.

McConney and another witness testified that all but two of the monthly checks were drawn from Trump's personal account. Yet even as jurors saw the checks and other documentary evidence, prosecutors did not elicit testimony Monday showing that Trump himself dictated that the payments would be logged as legal expenses — a designation that prosecutors contend was intentionally deceptive.

McConney acknowledged during cross-examination that Trump never asked him to log the reimbursements as legal expenses and never discussed the matter with him at all. Another witness, Deborah Tarasoff, a Trump Organization accounts payable supervisor, said under questioning that she did not get permission to cut the checks in question from Trump himself.

“You never had any reason to believe that President Trump was hiding anything or anything like that?” Trump attorney Todd Blanche asked.

“Correct,” Tarasoff replied.

The testimony followed Judge Juan M. Merchan's sober warning to Trump that additional violations of a gag order barring inflammatory out-of-court comments about witnesses, jurors and others closely connected to the case could land the former president behind bars.

The $1,000 fine imposed Monday marks the second time since the trial began last month that Trump has been sanctioned for violating the gag order. He was fined $9,000 last week — $1,000 for each of nine violations.

“It appears that the $1,000 fines are not serving as a deterrent. Therefore going forward, this court will have to consider a jail sanction,” Merchan said before jurors were brought into the courtroom. Trump's statements, the judge added, “threaten to interfere with the fair administration of justice and constitute a direct attack on the rule of law. I cannot allow that to continue.”

Trump sat forward in his seat, glowering at the judge as he handed down the ruling. When the judge finished speaking, Trump shook his head twice and crossed his arms.

Yet even as Merchan warned of jail time in his most pointed and direct admonition, he also made clear his reservations about a step that he described as a “last resort” and said he would only do so if prosecutors recommended it.

“The last thing I want to do is put you in jail,” Merchan said. “You are the former president of the United States and possibly the next president, as well. There are many reasons why incarceration is truly a last resort for me. To take that step would be disruptive to these proceedings, which I imagine you want to end as quickly as possible.”

The latest violation stems from an April 22 interview with television channel Real America's Voice in which Trump criticized the speed at which the jury was picked and claimed, without evidence, that it was stacked with Democrats.

Once testimony resumed, McConney recounted conversations with longtime Trump Organization finance chief Allen Weisselberg in January 2017 about reimbursing Cohen for a $130,000 payment intended to buy Daniels' silence over her account of a sexual encounter at a 2006 celebrity golf outing in Lake Tahoe, California.

Weisselberg “said we had to get some money to Michael, we had to reimburse Michael. He tossed a pad toward me, and I started taking notes on what he said,” McConney testified. “That's how I found out about it.”

“He kind of threw the pad at me and said, 'Take this down,'” said McConney, who worked for Trump's company for about 36 years, retiring last year after he was granted immunity to testify for the prosecution at the Trump Organization's New York criminal tax fraud trial.

A bank statement displayed in court showed Cohen paying $130,000 to Keith Davidson, Daniels' lawyer, on Oct. 27, 2016, out of an account for an entity Cohen created for the purpose.

Weisselberg's handwritten notes spell out a plan to pay Cohen $420,000, which included a base reimbursement that was then doubled to reflect anticipated taxes as well as a $60,000 bonus and an expense that prosecutors have described as a technology contract.

McConney's own notes, taken on the notepad he said Weisselberg threw at him, were also shown in court. After calculations that laid out that Cohen would get $35,000 a month for 12 months, McConney wrote: “wire monthly from DJT.”

Asked what that meant, McConney said: “That was out of the president's personal bank account.”

McConney testified that he had instructed Tarasoff to record the reimbursements to Cohen as a legal expense, reasoning that “we were paying a lawyer so I said to post it to legal expenses in the general ledger.”

McConney suggested it was his idea alone to log the payments that way, acknowledging under cross-examination that Trump never directed him to log Cohen's payments as legal expenses, nor did Weisselberg relay to him that Trump wanted them logged that way.

“Allen never told me that,” McConney testified. In fact, McConney said he never spoke to Trump about the reimbursement issue at all. Regardless, Trump lawyer Emil Bove suggested, the “legal expense” label made sense — and was not duplicitous — because Cohen was a lawyer at the time.

“OK,” McConney responded, prompting laughter throughout the courtroom. “Sure. Yes.”

After paying the first two checks to Cohen through a trust, the remainder of the checks, beginning in April 2017, were paid from Trump's personal account, McConney testified.

With Trump, the only signatory to that account, now in the White House, the change in funding source necessitated “a whole new process for us,” McConney added.

Tarasoff, the other witness who testified Monday, said that once Trump became president, checks written from his personal account had to first be delivered, via FedEx, “to the White House for him to sign.”

The checks would then return with Trump's Sharpie signature. “I'd pull them apart, mail out the check and file the backup,” she said, meaning putting the invoice into the Trump Organization's filing system.

Prosecutors are continuing to build toward their star witness, Cohen, who pleaded guilty to federal charges related to the hush money payments, went to prison and has been disbarred. He is expected to undergo a bruising cross-examination from defense lawyers seeking to undermine his credibility with jurors.