Transcript for President's campaign taking legal action against Omarosa

We begin with the war of words between president trump and omarosa. He brought her with him from his reality TV show, but tonight, omarosa revealing another piece of audio, this time, of a conversation she had about campaign aides about then-candidate Donald Trump and the possibility of a tape on which trump uses the n-word. This recording made public just hours after the president accused omarosa of lying. And tonight, the white house is pressed. Can you guarantee the American people there will be no such tape? ABC's chief white house correspondent Jonathan Karl leading us off. Reporter: Tonight, president trump's campaign is taking legal action to silence omarosa, as the president himself launches a vicious counterattack, calling his former senior adviser a "Crazed, crying lowlife," adding, "Good work by general Kelly for quickly firing that dog!" Is this any way for a president to talk about any American, let alone somebody that he hired and made the highest ranking African-American woman that served in his white house? I think the president is certainly voicing his frustration with the fact that this person has shown a complete lack of integrity. Reporter: But why did he hire her? I mean, why did he hire somebody he's describing as a dog, as a lowlife? The president wanted to give her a chance. Reporter: Of course, the president used to talk glowingly about omarosa. Witness the call she secretly recorded just after she was fired. Omarosa, what's going on? I just saw in the news that you're thinking about leaving. What happened? General Kelly -- general Kelly came to me and said that you guys wanted me to leave. No. Nobody even told me about it. Nobody. Wow. You know, they run a big operation. But I didn't know it. I didn't know that. I don't love you leaving at all. Reporter: Eight months later, she is now leveling explosive allegations. That there is a recording of trump during his "Apprentice" days using the n-word, and that his own campaign advisers knew about it. No one doubted he said it. And in fact, they had worked to try to suppress this tape for so long. And everyone says, he said it. He's embarrassed. Reporter: She provided CBS news with another secretly recorded conversation, this one featuring trump campaign aides in 2016 seeming to discuss whether the president had been caught on tape using the n-word. I'm trying to find out at least what context it was used in to help us maybe try to figure out a way to spin it. Reporter: Another aide says she asked the president about it. I said, "Well, sir, can you think of any time that this might have happened?" And he said, "No." Well, that's not true. So -- He goes, "How do you think I should handle it?" And I told him exactly what you just said, omarosa, which is, "Well, it depends on what scenario you're talking about." And he said, "Well, why don't you just go ahead and put it to bed?" He said it. No, he said it. He's embarrassed. Reporter: Via Twitter today, the president said the executive producer of "The apprentice" assured him there are "No tapes" of him using "Such a terrible and disgusting word," adding, "I don't have that word in my vocabulary and never have." But at the white house press briefing this afternoon -- Can you stand at the podium and guarantee the American people they'll never hear Donald Trump utter the n-word on a recording in any context? I can't guarantee anything. But I can tell you that the president addressed this question directly. I can tell you I have never heard it. Jon Karl with us tonight live at the white house. Jon, you reported there the president tweeted "I don't have that word in my vocabulary and never have. She made it up." And Jon, tonight, omarosa is saying she's been interviewed by special counsel Robert Mueller. I'm curious when your sources are saying about that. Reporter: No comment whatsoever from the white house. But sources close to the white house, David, say that the special counsel never requested an interview from omarosa while she was an employee here at the white house. Of course, she left in December and nobody here can say for sure whether or not Mueller would have requested an interview after she left. Jon Karl leading us off tonight. Jon, thank you.

This transcript has been automatically generated and may not be 100% accurate.