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.

With Donald Trump following along from the defense table, head cocked slightly to the side, David Pecker described the negotiations conducted with Karen McDougal to purchase the exclusive rights to her story about an alleged year-long relationship with Trump.

Pecker said that Trump's attorney Michael Cohen authorized negotiations to begin, then during those negotiations, "Michael was very agitated," constantly asking "Why is this taking so long?"

"To purchase the lifetime rights to Karen McDougal was going to cost $150,000. Plus Karen wanted to restart her career. She wanted to write for the celebrity magazines. She wanted to be on the cover of the life and fitness titles. She had a major problem when her breast implants were removed and she wanted to write about that," Pecker testified.

Pecker said he asked Cohen, "Who is going to reimburse me for this?" He said Cohen responded "Don't worry about it, I'm your friend the boss will take care of it.'"

When prosecutor Josh Steinglass asked Pecker who "the boss" was, Pecker answered "The boss would have been Donald Trump"

Prosecutors then displayed for the jury the contract with McDougal, dated August 5, 2016. It awarded AMI, the Enquirer's parent company, the rights to her story of a relationship she had "with any then-married man." Pecker said "she was referring to Donald Trump."

Pecker testified he needed to "validate" the amount of money AMI was going to pay, so the contract included other provisions, like having McDougal write monthly columns on aging and fitness.

"With respect to campaign laws, I wanted to have the contract be a record that stipulates the services she was going to perform for American Media had a basis for it, the $150,000," Pecker said.

"Was it your primary purpose to buy the life rights?" Steinglass asked. "Yes it was," Pecker responded.

"Were the other provisions to disguise the true nature of this contract?" Steinglass asked. "Yes," Pecker replied, letting out a sigh.