On his way into the courtroom for the day's proceedings, Trump once again alleged that the trial constitutes election interference, claiming that the proceedings are unfairly keeping him off the campaign trail.

"Everybody knows that I'm here instead of being able to be in Pennsylvania and Georgia and lots of other places campaigning, and it's very unfair," he told reporters.

"It's a very, very sad day in America," he said. "I can tell you that."

The former president is seated at the defense table between his lawyers Todd Blanche and Emil Bove.

-Mike Pappano

The proceedings are underway in former President Donald Trump's hush money trial. Trump and Manhattan District Attorney Alvin Bragg are both in the courtroom.

Three prosecutors -- Joshua Steinglass, Matthew Colangelo, and Susan Hoffinger -- are seated at the counsel table.

Bragg is seated in the front row of the gallery with approximately a dozen lawyers and staff from his office.

The first witness prosecutors with the Manhattan DA's office plan to call is former National Enquirer publisher David Pecker, according to two sources familiar with the matter.

ABC News previously reported that prosecutors planned to call Pecker as a witness, but sources now say he's expected to be the first witness to take the stand.

Pecker served as the longtime chief executive of American Media Inc., which published the National Enquirer.

Shortly after Trump announced his 2016 presidential campaign, Pecker met with Trump and agreed to act as the "eyes and ears" of the campaign by looking out for and killing negative stories about Trump, according to the Manhattan DA.

As part of the arrangement, Pecker allegedly directed a deal to pay $30,000 to a former Trump Tower doorman regarding the false allegation that Trump allegedly fathered a child out of wedlock, prosecutors say. Then-Trump attorney Michael Cohen allegedly insisted that the deal stay in place even after AMI discovered the allegation was false, and AMI paid the doorman, according to the Manhattan DA.

-Katherine Faulders

After a week-long selection process, the jurors in Donald Trump's New York hush money case are scheduled to hear opening statements this morning in the first criminal trial of a former U.S. president.

To prove their case, lawyers for Manhattan District Attorney Alvin Bragg need to convince twelve jurors beyond a reasonable doubt that Trump repeatedly falsified records to unlawfully influence the 2016 presidential election.

"This case has nothing to do with your personal politics or your feelings about a particular political issue," prosecutor Joshua Steinglass told prospective jurors on Thursday. "It's not a referendum on the Trump presidency, a popularity contest, or any indication of who you plan to vote for this fall. This case is about whether this man broke the law."

Trump's lawyers are expected to focus their efforts on going after the credibility of prosecution witnesses, suggesting the case itself is politically motivated and arguing that the former president never intended to commit a crime.

After court resumed for the afternoon session, David Pecker retook the stand.

The former National Enquirer publisher testified that six months after Donald Trump became president, Trump hosted a "thank-you dinner" for Pecker and some of his business associates.

After taking photos in the Oval Office -- "Jared Kushner was there, Sean Spicer was there" Pecker said -- Trump asked Pecker to walk with him along the colonnade "past the Rose Garden," Pecker recalled. The jury saw a photo of the two men on that walk.

Trump said that on that walk, Trump asked Pecker, "How's Karen doing?" referring to Karen McDougal, who the National Enquirer had paid to catch-and-kill her story claiming a year-long relationship with Trump.

"She's doing well. She's quiet. All's going good," Pecker recalled responding.

Eight months later, in March 2018, Pecker said Trump called him about a television interview McDougal had conducted.

"He said 'Did you see the Anderson Cooper interview with Karen McDougal?' I said yes. He said, 'I thought we had an agreement with Karen that she can't give any interviews or be on any television shows.' So I said yes we have an agreement, but I amended it," said Pecker, who testified earlier that he had done so following the election.

Pecker testified that Trump was very upset. "He couldn't understand why," Pecker said. "He couldn't believe that I did it."

Pecker said Trump also called him after Stormy Daniels appeared on a television interview a short while later.

"He said, 'We have an agreement with Stormy Daniels that she cannot mention my name or do anything like this, and each time she breaches the agreement it's $1 million penalty,'" Pecker said.