President Donald Trump must immediately fire all Obama administration appointees and employees because "we are in a very dangerous situation," David Horowitz, author of The New York Times best-seller "Big Agenda: President Trump's Plan to Save America," said Thursday.

"We're in a civil war," he told Sean Hannity on Fox News. "The Democrats have adopted the slogan 'resistance.'

"Trump needs to fire all the Democratic appointees in these departments."

Find out Obama's next attack on Trump – More Info in "Big Agenda" – See More Here

Horowitz's "Big Agenda" — the first major book on the Trump administration — still holds its No. 5 spot for hardcover nonfiction books. It has been on the list for several weeks.

The book, released the week of Trump's inauguration, has also hit the No. 1 bestseller in several Amazon categories.

Horowitz singled out the Justice Department, and the intelligence agencies that fall within its purview, in light of the numerous negative leaks about the Trump administration.

"Ninety-nine percent of the Justice Department's employees gave money to the Democrats," he told Hannity. "We know the Democrats are untrustworthy on national security."

"Big Agenda: President Trump's Plan to Save America" is available at bookstores everywhere – or Get yours FREE from Newsmax – Click Here Now