In a series of tweets early Saturday, President Donald Trump slammed author Michael Wolff and described himself as "a very stable genius." He also tweeted about "Russian collusion," the "Fake News Mainstream Media" and the unemployment rate for African-Americans, among other topics.

"Michael Wolff is a total loser who made up stories in order to sell this really boring and untruthful book," Mr. Trump tweeted, seemingly referring to "Fire and Fury," Wolff's bombshell expose on the Trump administration. "He used Sloppy Steve Bannon, who cried when he got fired and begged for his job. Now Sloppy Steve has been dumped like a dog by almost everyone. Too bad!"

It's his latest pushback against the book that portrays him as a leader who doesn't understand the weight of the presidency. In the book, former aide Steve Bannon questions Mr. Trump's competence.

Mr. Trump said "the Democrats and their lapdogs, the Fake News Mainstream Media, are taking out the old Ronald Reagan playbook and screaming mental stability and intelligence....."

"Throughout my life, my two greatest assets have been mental stability and being, like, really smart," Mr. Trump tweeted. "Crooked Hillary Clinton also played these cards very hard and, as everyone knows, went down in flames. I went from VERY successful businessman, to top T.V. Star ... to President of the United States (on my first try). I think that would qualify as not smart, but genius....and a very stable genius at that!"

Mr. Trump also posted about the unemployment rate for African-Americans, which in December was at the lowest level since the government started tracking such data in 1972. The reasons for the record low range from a greater number of black Americans with college degrees to a growing need for employers in a tight job market to widen the pool of people they hire from.

"The African American unemployment rate fell to 6.8%, the lowest rate in 45 years. I am so happy about this News!" Mr. Trump said.