The New York judge in Donald Trump's criminal trial warned him against intimidating jurors on Tuesday after he mumbled and gestured while one prospective juror was being questioned.
The former president also appeared to doze off during proceedings, court reporters said.
Justice Juan Merchan said he heard Mr Trump making remarks while his lawyers were questioning a prospective juror, and admonished the Republican presidential hopeful.
The first seven of 12 jurors were eventually empanelled.
“I will not have any jurors intimidated in the courtroom,” Mr Merchan said.
It was the second day of Mr Trump's trial on 34 felony counts of falsifying business records to cover up a hush money payment scheme.
He is accused of sending people payments to shut down possible scandals during the 2016 presidential campaign, including one of $130,000 to adult film star Stormy Daniels, who said she had an affair with Mr Trump years earlier.
He has pleaded not guilty and denies the affair.
No other former US president has had to stand trial. New York state law makes it mandatory for the defendant to be present for every day of a legal proceeding.
“This is a trial that should have never been brought,” Mr Trump told reporters outside the courtroom.
He lashed out against President Joe Biden, his Democratic rival in the November election, and what he called the “Trump-hating judge”.
The trial means Mr Trump must spend most of his time over the next several weeks in court, instead of on the campaign trail.
The New York Times on Monday reported that he “appeared to nod off a few times” with “his head drooping on to his chest”, and a Law360 reporter said they observed Mr Trump falling asleep again on Tuesday.
Mr Trump has repeatedly referred to Mr Biden as “Sleepy Joe”.
Mr Trump has in the past tested the limits of judges and is under a partial gag order from Mr Merchan, limiting what he can say about witnesses, court staff and family members connected to the New York case.
After a preliminary phase where more than half of the initial pool of 96 jurors stepped out over their beliefs that they could not be impartial, defence lawyers and prosecutors began questioning people to fill a panel of 12.
Jury selection in Manhattan, a largely Democratic borough of New York City, could prove to be tricky.
Defence lawyers pressed prospective jurors about their past social media posts.
The jurors selected include a man originally from Ireland who enjoys doing “anything outdoorsy” and watches MSNBC and Fox News, an oncology nurse who enjoys taking her dog to the park, and a corporate lawyer who said he does not follow the news very closely.
Mr Merchan told the first six seated jurors that they did not need to return to court until next Monday, when opening statements could begin.
