Case Law Professor Bennett Gershman from Pace University said a possible arrest of former President Donald Trump would be unprecedented.

Trump posted on social media Saturday that his arrest is imminent, despite that there were no official announcements from any law enforcement agencies.

Trump also called on his supporters to protest as a New York grand jury investigates hush money payments to women who alleged sexual encounters with the former president.

"When he made that announcement, it seemed to me to solidify the allegations that were going to be brought against him," Gershman said. "No president or ex-president has ever been charged with a crime in our history. This is the first time this has ever happened. So this is, as I said, unprecedented. It's we can say it's something that is stunning, remarkable, but it's something that the vast majority of Americans realize over the last several years could happen because there's so many investigations going on."

Another witness is expected to testify before a grand jury on Monday in Manhattan.

It is not clear whether this would be the final witness before voting on a possible indictment.