WASHINGTON — White House press secretary Sarah Sanders said Tuesday that she could not "guarantee" that there are no recordings of President Donald Trump using the N-word.

"I’ve never heard him use that term or anything similar," Sanders said in response to a series of questions from NBC's Kristen Welker about whether he's ever used the racial slur. Asked if she could promise that Americans would never hear him say it on a recording, she declined. "I can’t guarantee anything, but I can tell you the president addressed this question directly," she said, though she acknowledged that she had never asked him the question herself.

The back-and-forth at Tuesday's White House briefing followed the publication of a book from former Trump aide Omarosa Manigault Newman, who says she was fired by chief of staff John Kelly because she was investigating rumors that Trump had used the word during tapings of "The Apprentice," his long-running NBC reality show. On Sunday, Manigualt Newman told NBC's Chuck Todd that she has since heard a recording of Trump saying it.

On Monday, the president took to Twitter to deny the existence of such a tape.

.@MarkBurnettTV called to say that there are NO TAPES of the Apprentice where I used such a terrible and disgusting word as attributed by Wacky and Deranged Omarosa. I don’t have that word in my vocabulary, and never have. She made it up. Look at her MANY recent quotes saying.... — Donald J. Trump (@realDonaldTrump) August 14, 2018

....such wonderful and powerful things about me - a true Champion of Civil Rights - until she got fired. Omarosa had Zero credibility with the Media (they didn’t want interviews) when she worked in the White House. Now that she says bad about me, they will talk to her. Fake News! — Donald J. Trump (@realDonaldTrump) August 14, 2018

Trump and his aides have continued to wage a rhetorical war on Manigualt Newman and her book, "Unhinged: An Insider's Account of the Trump White House."

On Tuesday morning, the president called Manigault Newman a "dog" on Twitter, which sparked another round of accusations that he employs racist language.

When you give a crazed, crying lowlife a break, and give her a job at the White House, I guess it just didn’t work out. Good work by General Kelly for quickly firing that dog! — Donald J. Trump (@realDonaldTrump) August 14, 2018

Sanders said Trump is an "equal opportunity" denigrator who "fights fire with fire."

"This has absolutely nothing to do with race and everything to do with the president calling out someone’s lack of integrity," she said. "The president has said similar things about a number of individuals, certainly, that are not African-American or any other minority."

Sanders said that she and other White House aides would quit their jobs "if at any point we felt that the president was who some of his critics claim him to be" and that he wouldn't have been able to form close relationships with other luminaries in the business and political worlds, including "Bill and Hillary Clinton," if he was.

"They attended his wedding," she said of Trump's former rival, whom he calls "Crooked Hillary," and her husband, the former president.

During the press briefing, Sanders said there was nothing unusual about the Trump administration's policy of asking staffers to sign nondisclosure agreements. "Other White Houses have had people sign NDAs. It's standard," she said.

Officials who have worked in prior administrations said Tuesday that that claim was not true.

Chris Lu, a former Obama White House cabinet secretary, told NBC News that nondisclosure agreements are not standard in presidential administrations and that no one in the Obama White House signed such an agreement. Lu says there are restrictions against releasing highly classified, sensitive information — but that falls under a security clearance, not an NDA.

Ari Fleischer, a White House press secretary under President George W. Bush, told The Washington Post that "Bush aides weren’t asked to sign such agreements unless they saw highly classified, sensitive information."

Sanders, when asked, would not say Tuesday whether she herself had signed a nondisclosure agreement.