Former President Donald Trump is expected to be joined by his son Don Jr. in court today.

It would mark the first time Don Jr. has attended the trial.

As has been the case over the last several days in court, a number of Republican lawmakers are expected to attend today's proceedings in support of Trump.

A day after Judge Judge Juan Merchan threatened to remove him from the witness stand, former federal prosecutor Robert Costello will resume his testimony this morning as the second witness in Donald Trump's defense case.

Costello is expected to be the final defense witness before Trump's lawyers rest their case today.

Yesterday, Costello told jurors about his meetings and phone calls with Michael Cohen in 2018 after FBI agents raided his office and hotel room. Costello advised Cohen and helped pass messages to the Trump, according to Cohen, but never formally represented him as his lawyer.

"Michael Cohen said, numerous times, that President Trump knew nothing about those payments, that he did this on his own, and he repeated that numerous times," Costello testified about the hush money payment to adult film actress Stormy Daniels that sits at the center of the case.

Cohen told the jury that he lied to Costello about Trump's involvement in the scheme to use hush-money payments to hide information from voters.

Costello's reactions to Judge Merchan after taking the stand yesterday afternoon -- responding "jeez" to a sustained objection, rolling his eyes at the judge, and appearing to staring him down -- prompted Merchan to clear the courtroom before threatening to remove Costello from the witness stand.

While defense lawyers suggested yesterday that they would not call Trump to the witness stand, they will likely have to confirm a final decision about the defendant's testimony -- or lack thereof -- before they rest their case.

Judge Merchan has scheduled a charge conference at 2:15 p.m. ET to hear arguments over how to instruct the jury about the law in the case.

Donald Trump, exiting the courtroom, commented on the chaotic scene this afternoon when Judge Juan Merchan cleared the courtroom so he could admonish defense witness Robert Costello.

"A totally conflicted judge who just did something that nobody's ever seen -- and the press is not happy -- I don't imagine they just got thrown out of the courthouse. Nobody's ever seen anything quite like it," Trump said.

Trump also said he was unhappy that the judge decided to limit the testimony of the defense's expert witness on election law.

"We're not allowed to put it in an expert witness," Trump said. "Nobody's ever heard of it before. You know, election law is very complicated, actually."

-ABC News' Kelsey Walsh and Mike Pappano

Responding to the defense's motion to dismiss the case, prosecutor Matthew Colangelo Colangelo argued that Trump, at a minimum, can be found responsible for the actions of his accomplices if he set the action into motion.

"At minimum a rational jury can conclude beyond a reasonable doubt that they all contained false information," Colangelo said of the business records that recorded Michael Cohen's hush money repayment as legal expenses.

Trump, at the defense table, jotted down notes as Colangelo spoke.

"The trial evidence overwhelmingly supports each element of the offense," Colangelo argued.

Defense attorney Todd Blanche pushed the theory that Trump has argued since the first days of the trial: How else would Trump describe a payment to his lawyer other than a legal expense?

"It's hard to imagine what book -- how was this supposed to be booked by Ms. Tarasoff," Blanche asked about Trump Organization accounts payable supervisor Deborah Tarasoff.

Judge Merchan said he will reserve his decision on the motion.

Court was then concluded for the day.

Throughout his cross-examination this morning, defense attorney Todd Blanche has attempted to legitimize the repayment arrangement between Trump and Cohen in 2017.

Prosecutors have argued that Trump falsified business records by describing a reimbursement for the Stormy Daniels payment and other expenses as payment for legal services pursuant to a retainer agreement, even though Cohen never had a retainer agreement with Trump.

Blanche emphasized all the legal work that Cohen did for Trump and his family in 2017. He also showed the jury an email from Allen Weisselberg, where he requested Cohen to "please prepare the agreement we discussed so we can pay you monthly."

Amid frequent objections, Blanche has referenced the "agreement" mentioned above as a "retainer agreement," though Cohen never had a formal retainer agreement with Trump.

Pursuant to the "agreement," Cohen said he received nine checks directly from Trump in 2017.

"That would have been nine checks -- 35,000 a piece," Cohen said.