Donald Trump's former lawyer and "fixer," Micheal Cohen, will testify before a Manhattan grand jury Monday, a crucial witness in the investigation probing the origins of a hush-money payment just prior to the 2016 presidential election.

Cohen is alleged to have arranged and made the payments on behalf of the former president. He told journalists outside the courtroom Monday that Trump "needs to be held accountable for his dirty deeds."

"My goal is to tell the truth," Cohen, Trump's former right-hand man turned prime challenger, told reporters.

In 2018, Cohen pled guilty to charges stemming from a $130,000 hush-money payment to adult film actress Stormy Daniels to keep her quiet about an alleged sexual affair with Trump. The payment occurred on the eve of election day 2016, and Cohen was later reimbursed in full by the Trump company.

Trump has consistently denied any involvement with Daniels and has disparaged the investigation into the payment from the beginning. The probe is being conducted by the Manhattan District Attorney's Office.

Cohen's appearance in court is the latest sign that an indictment of the former president may be on the horizon and coupled with last week's invitation for Trump to testify on his own behalf.

Trump has not officially declined the offer, but during an appearance Monday on ABC's "Good Morning America," a lawyer representing the former president said they plan to "wait and see," while simultaneously casting Trump as a victim.

"This was a plain extortion and I don't know since when we've decided to start prosecuting extortion victims," Trump lawyer Joseph Tacopina said. "He's denied — vehemently denied — this affair. But he had to pay money because there was going to be an allegation that was going to be publicly embarrassing to him, regardless of the campaign."