Trump tweets at author of latest White House tell-all book during live interview

The author of a new tell-all book on the White House was on national television Tuesday morning promoting it -- and had just finished discussing how the president's senior policy adviser Stephen Miller once told him he'd be happy if "not a single refugee foot ever touched American soil" -- when the president finally tweeted about him.

Just a few minutes after, Trump's campaign announced legal action would follow.

President Donald Trump called Cliff Sims, a former director of White House message strategy, "a low level staffer that I hardly knew" who wrote "yet another boring book based on made up stories and fiction."

"He pretended to be an insider when in fact he was nothing more than a gofer. He signed a non-disclosure agreement. He is a mess!" Trump also said in the tweet, his first public comment on Sims since he began promoting the book on different TV shows Monday.

"Nice," Sims said on CNN's "New Day," where he was being interviewed when Trump's tweet went out. "There it is."

In writing his book, "Team of Vipers," Sims joined ranks with former White House press secretary Sean Spicer, former campaign manager Corey Lewandowski, former deputy campaign manager David Bossie and former aide Omarosa Manigault Newman, all of whom have written books on their time in the administration at varying levels of detail and, according to the White House, veracity.

Just minutes earlier, CNN's host Alisyn Camerota had asked Sims if he'd signed a non-disclosure agreement that may have barred him from sharing the kind of detailed, controversial information he put in his book.

"The truth is I kinda don't remember," Sims said, laughing. "I assume I signed whatever Sean Spicer signed in the White House, I assume I signed whatever Corey Lewandowski and Dave Bossie signed on the campaign, those folks have written books. But I just really don't remember," Sims said.

Within 20 minutes, both the president and the chief operating officer for Trump's campaign Michael Glassner had pointed out the NDA. The campaign was "preparing to file suit against Cliff Sims for violating our NDA," Glassner tweeted.

The Trump campaign announced similar actions against Manigault Newman in August of last year. Both the book, "Unhinged: An Insider's Account of the Trump White House," and recordings she released of Trump violated her NDA, the campaign said.

According to Manigault Newman's attorney John Phillips, the suit is still in arbitration.

ABC News' Meridith McGraw contributed to this report.