The judge in Donald Trump's hush money trial declined Monday to broaden the scope of testimony that the defense can elicit from a potential expert witness, Bradley A. Smith, a former Bill Clinton-appointed Republican Federal Election Commission member.

Judge Juan M. Merchan echoed his pretrial ruling that, if called, Smith can give general background on the FEC - its purpose, background and the laws it enforces - and the definitions of such terms as "campaign contribution."

Merchan rejected the defense's renewed efforts to have Smith define three terms in federal election law, saying it would breach rules preventing expert witnesses from interpreting the law. Nor can Smith opine on whether the former president's alleged actions violate those laws, Merchan said.

If Smith were to testify about those issues, Merchan said, the prosecution would then be permitted to call an expert of its own. That would result in a "battle of the experts," the judge said, "which would only serve to confuse and not assist the jury."

Smith is a law professor, and that there often are guardrails around expert testimony on legal matters, on the basis that it's up to a judge - not an expert hired by one side or the other - to instruct jurors on applicable laws in a case.

"Good morning Mr. Trump," Judge Juan Merchan said as he gaveled in the proceedings.

"It's become apparent that we are not going to be able to sum up tomorrow," the judge said after taking the bench.

Merchan said it's more likely summations will take place next Tuesday, after procedural matters and the Memorial Day break.

"Either have a long break now or a long break then, and unfortunately the calendar is what it is," the judge said.

Prosecutors have entered the courtroom for Day 19 of the trial.

Trump has arrived with his entourage.

Before entering, the former president addressed reporters but ignored their questions about whether he'll testify in the trial.

Donald Trump's former lawyer Michael Cohen will return to the witness stand for the final time before prosecutors rest their case against the former president in Trump's criminal hush money case Monday.

Cohen last week described Trump as being deeply involved in a scheme to hide information from voters ahead of the 2016 election, but a stinging line of cross-examination may have damaged Cohen's overall credibility with the jury.

Prosecutors plan to rest their case Monday morning, and defense attorneys have not yet declared who they plan to call to testify -- including whether Trump will testify in his own defense.

Defense lawyers have suggested they might call Bradley Smith -- an expert on federal campaign finance laws -- and have left the door open to call rebuttal witnesses.

During his cross-examination of Cohen on Thursday, defense attorney Todd Blanche accused him of lying about an alleged phone call with Trump related to the Stormy Daniels' hush money payment.

Cohen testified that on Oct. 24, 2016, he placed a phone call to Trump's security guard Keith Schiller, who passed the phone to Trump so he and Cohen could "discuss the Stormy Daniels matter and the resolution of it."

On Thursday, Blanche presented evidence to suggest that Cohen lied about the purpose of the phone call, arguing that Cohen actually called to complain to Schiller about a teenage prank caller.

Jurors saw text messages between Cohen and the prank caller from the same day as the alleged phone call between Cohen and Trump.

"This number has just been sent to secret service for your ongoing and continuous harassment to both my cell as well as to the organizations main line," Cohen texted the teenager.

"It wasn't me," the 14-year-old prank caller replied. "My friend told me to call."

Jurors also saw text messages between Cohen and Schiller ahead of their phone call at 8:02 p.m.

"Who can I speak to regarding harassing calls to my cell and office. The dope forgot to block his call on one of them," Cohen texted Schiller.

"Call me," Schiller texted Cohen at 8:02 p.m..

When confronted with the alleged inconsistency, Cohen stood by his initial testimony, arguing he spoke to Trump about the hush-money payment in addition to talking to Schiller about the prank caller.

"That was a lie, you did not talk to President Trump on that night, you talked to Keith Schiller about what we just went through; you can admit it?" Blanche confronted Cohen while raising his voice.

"No, sir, I can't. I am not certain that is accurate," Cohen responded.

While the cross-examination may have broadly damaged Cohen's credibility, the specific phone call emphasized by Blanche was just one of many conversations between Cohen and Trump related to the Daniels' payoff. Cohen testified that he had multiple other phone calls and in-person meetings with Trump -- in both Trump Tower and the Oval Office -- where Cohen claimed they discussed how to approach Stormy Daniels' allegations, the plan for Cohen to make the payment, and the scheme to reimburse Cohen in 2017.

Trump, for his part, has repeatedly signaled his willingness to testify during the trial.

"I would have no problem testifying," Trump told ABC News on March 25. "I didn't do anything wrong."

"I would testify, absolutely," Trump said on April 12. "It's a scam. It's a scam. That's not a trial. That's not a trial. That's a scam."

However, Trump appeared to back away from the idea earlier this month, falsely telling reporters that the limited gag order in the case -- which prohibits extrajudicial statements about witnesses and jurors -- prevents him from testifying.

The next day in court, Judge Juan Merchan directly addressed Trump to clarify that he has an "absolute right" to testify and that the gag order does not apply to his statements in court.

"I want to stress, Mr. Trump, that you have an absolute right to testify at trial, if that is what you decide to do after consultation with your attorneys," Merchan said.