President Donald Trump could end up testifying under oath in the Russia probe, and that, over the course of the investigation being conducted by the special counsel Robert Mueller, has unsettled Trump's defense lawyers.

In the roughly 15 months since Mueller was appointed, multiple news outlets have reported on the negotiations between the two sides that would set the terms for Trump to testify.

The biggest question has been whether or not Trump's lawyers should allow their client to be interviewed by Mueller's team under oath, given Trump's tendency to speak off the cuff and say things that are contradictory or untrue.

Lawyer Glenn Zeitz, who deposed Trump in a 1990s court case, talked about the experience in a CNN interview that aired Friday night.

Before he was president, private citizen Donald Trump sat for several depositions in legal cases related to his businesses. One attorney who deposed Trump in the 1990s told CNN about the experience in a segment that aired Friday night.

Attorney Glenn Zeitz questioned Trump under oath in an eminent-domain case in which Trump sought to take control of an elderly woman's Atlantic City, New Jersey, property so he could build a parking lot for one of his casinos.

When asked to describe Trump's demeanor during his 1996 deposition, Zeitz said, "Donald was the Donald you see now."

"He walks in, he wants to take over, he wants to make the deposition his deposition, even though it's mine. He tries to control the questioning," Zeitz said.

The lawyer recalled the moment he realized he was starting to get under Trump's skin: "He's calling me a 'third-rate lawyer,' I though it was pretty good that he was saying that because it meant that finally, after almost two hours, that I had gotten to him."

Zeitz described some of Trump's language patterns when it came to answering questions. "He will add things on, he'll make self-serving statements."

"If I asked Donald a question, I said 'Donald, what time is it?' He'd probably tell me how to build a clock. He was grossly unprepared, or he was just deliberately being evasive,'" Zeitz said.

Watch the interview below:

Much has been said and written about the possibility that President Donald Trump could testify under oath in the ongoing Russia investigation.

One of the key concerns for Trump's lawyers is whether or not they should allow the president to sit with prosecutors led by Robert Mueller, the special counsel overseeing the federal probe.

That's been the subject of much debate among the president's attorneys — some of whom worry Trump could encounter more legal exposure if he talks to Mueller, because of Trump's tendency to speak off the cuff and say things that are contradictory or untrue.

Mueller and Trump's legal team are currently negotiating terms for a sit-down interview that would likely cover topics ranging from his campaign's ties to Russia and obstruction of justice.