'This is not a conversation': Read heated exchange between Judge Merchan, Robert Costello

Fireworks broke out Monday between Judge Juan Merchan and a witness in Donald Trump's hush money trial, prompting the judge to clear the room and suggest the witness could be held in contempt.

Trump is on trial for 34 counts of falsifying business records. Prosecutors rested their case Monday after spending weeks trying to show the former president reimbursed his former lawyer Michael Cohen for paying porn star Stormy Daniels $130,000 in 2016, and disguised it as a legal expense to cover up a campaign finance violation.

Trump's defense team called Republican lawyer Robert Costello as their second witness. Costello is a key witness for the defense, as Cohen said Costello tried to act as a "back channel" to Trump in the White House. But after numerous objections from the prosecution were sustained, Costello seemed to get frustrated on the witness stand.

What followed was possibly the most dramatic moment of the trial yet:

Trump trial:Historic Trump trial heading to jury after prosecutors, defense lawyers rest:

'Jeez' Heated exchange prompts Merchan to clear the courtroom

'Jeez!' Costello said in the witness box, at a normal volume − but with an exasperated tone − after a sustained objection.

"Sorry?" "I'm sorry?" Merchan said heatedly to Costello. Costello then said "strike it," seeming to refer to striking his own testimony from the court record.

Costello continued testifying, and then he dramatically sighed after another objection was sustained. Merchan then excused the jurors from the courtroom and said to Costello:

 "I want to discuss proper decorum in my courtroom." Costello said when jurors left.

"Right," Costello responded.

"If you don't like my ruling, you don't say, 'Jeez!'" Merchan continued.

He reminded Costello, who is a veteran lawyer, that Costello also isn't permitted to say, "Strike it," because Merchan is the only one in the courtroom with the power to strike testimony. Merchan also made reference to Costello rolling his eyes.

"Do you understand that?" Merchan asked Costello, who was sitting within six feet of the judge, in the witness box to the judge's left.

Merchan then said to Costello in an inflamed tone: "Are you staring me down right now?"

"Clear the courtroom, please. Clear the courtroom," the judge then ordered. Court security officers then forced all reporters to leave the courtroom.

Transcript shows what Merchan said to Costello out of press earshot

THE COURT:

"Let the record reflect that it's now five after four. Let the record also reflect that the court officers had great difficulty clearing the courtroom, because the courtroom is made up primarily of the press.

"And I can appreciate that the press wants to be present for every part of these proceedings, therefore, this record is not sealed. The press will have access to this record.

"The fact that I had to clear the courtroom and that the court officers, including the Captain, had great difficulty clearing the courtroom, and that there was argument back and forth between the press and including counsel for the press, goes to why I had to clear the courtroom in the first place.

"And that is, sir, your conduct is contemptuous right now. I'm putting you on notice that your conduct is contemptuous. If you try to stare me down one more time, I will remove you from the stand.

"I will strike his entire testimony; do you understand me?"

EMIL BOVE (a Trump defense lawyer): "Yes, Judge. I understand."

THE COURT: "Listen to the question and answer the question."

THE WITNESS: "Can I say something, please?"

THE COURT: "No. No. This is not a conversation."

THE WITNESS: "Okay."

THE COURT: "All right. Let's -- we can bring the press back in, please."

Read Monday's proceedings in the hush money trial

Who is Robert Costello?

Robert Costello is a former federal prosecutor and Trump ally who has been called to challenge testimony from prosecution star witness Michael Cohen. According to Cohen, Costello tried to create a back channel of communication to Trump through former New York mayor Rudy Giuliani in 2018, after the FBI raided Cohen's office.

"I swear to God, Bob, I don't have anything on Donald Trump," Cohen told Costello at the time, according to Costello's Monday testimony. Cohen himself testified that he never told Costello about Trump's alleged involvement in hush money payments ahead of the 2016 presidential election.