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.

Former National Enquirer publisher David Pecker described one of the most heated moments so far during the catch-and-kill arrangement between him, Donald Trump and Trump's then-attorney Michael Cohen.

When Cohen approached Pecker with a plan to reimburse the National Enquirer for buying the exclusive rights to Karen McDougal's story, the two men drew up paperwork in which Cohen would repay the Enquirer's parent company, AMI, through a shell company he created, Pecker said.

But Pecker testified that he had a change of heart after consulting with his general counsel.

"I called Michael Cohen and I said to him that the agreement we signed -- the deal was off. I am not going forward, it is a bad idea," Pecker testified. "I want you to rip up the agreement."

"He was very, very, angry. Very upset, screaming basically at me. And I said, I'm not going forward with this agreement, rip it up," Pecker said.

Pecker said Michael Cohen then brought up "the boss."

"And Michael Cohen said, the boss is going to be very angry with you. And I said, I'm sorry, I am not going forward. The deal is off," Pecker recounted. "And he said, I can't believe it. I'm a lawyer, I'm your friend. I don't understand why you're not going forward. I said I am not going forward. Period."

Pecker previously described at length that he was aware that the National Enquirer's payment to Karen McDougal in order to catch and kill her story for the benefit of Trump's campaign would amount to an illegal campaign contribution -- softening his tone when he testified to this.