Judge Juan Merchan ruled that prosecutors can grill former President Donald Trump on his past legal issues and violations of gag orders if he chooses to take the witness stand during his Manhattan criminal hush money trial.

Merchan briefed the courtroom on this decision, shortly before the prosecution and defense attorneys gave their opening statements to a jury of 12 Manhattenites, on Monday morning.

The prosecution will be allowed to ask Trump about civil court cases brought forward by the Manhattan District Attorney's office and by writer E. Jean Carroll.

Trump was found liable for sexually abusing Carroll and then defaming her when the writer came forward with the assault allegation. Merchan specifically mentioned the defamation suit, but not the sex abuse case during his remarks on Monday.

The Manhattan District Attorney's office won a $454 million judgment against Trump after they sued the former president for falsely inflating business records to gain more favorable loan terms.

Prosecutors are also allowed to question Trump about the 2018 civil court decision that resulted in the dissolution of the Donald J. Trump Foundation, due to financial irregularities. The former president's history of violating gag orders is also on the table - an issue that may be of particular interest, as prosecutors allege that Trump recently violated the gag order intended to protect witnesses and jurors in this trial.

Trump reportedly shook his head when Merchan mentioned that he was fined $15,000 for violating a gag order, during his civil trial.

Earlier this month, Trump told a group of reporters at Mar-a-Lago that he intended to take the witness stand - even though he cannot be legally compelled to testify against himself.

"I'm testifying. I tell the truth," he said. "I mean, all I can do is tell the truth. And the truth is that there's no case. They have no case."

Prosecutors do not have free reign to discuss all of Trump's legal woes - Merchan ruled that they can not question him about the Trump Organization's tax fraud convictions and the Florida sanction he received for filing frivolous lawsuits against Hillary Clinton.