Donald Trump is not only a childlike bungler unfit to be president — he’s also a lousy father and chronically wayward husband, according to an explosive new book that’s rocked the White House.

In “Fire and Fury: Inside the Trump White House,” author Michael Wolff calls Trump “an absentee father” to his five children and “a notorious womanizer” who rarely interacted with his wife, Melania.

“Donald Trump’s marriage was perplexing to almost everybody around him. He and Melania spent relatively little time together. They could go days at a time without contact, even when they were in Trump Tower together,” he wrote.

Often, he added, she didn’t know where he was — the couple slept in separate bedrooms — and didn’t seem to care.

“He was a notorious womanizer, and during the campaign became possibly the world’s most famous masher,” Wolff wrote, referring to the infamous “Access Hollywood” tape, in which Trump boasted about forcibly kissing women and grabbing them “by the p—y.”

Trump openly referred to the former model, who is 24 years younger than the 71-year-old president, as a ”trophy wife” in front of others, Wolff wrote.

And he shared a theory with pals that the greater the difference in age between an older man and younger woman, the less concerned the younger woman was about infidelity, according to the book, which was released Friday, four days ahead of schedule.

As a parent, Trump was “an absentee father for his first four children” and “was even more absent for his fifth, Barron, his son with Melania,” the author declared.

But he also lavished her with everything a billionaire could buy, and subscribed to the theory that “a happy wife is a happy life,” he wrote.

The thrice-married Trump also told friends that he had settled on a philosophy to live by — “Do your own thing,” according to Wolff.

Melania, he said, was aghast at the prospect of her husband winning the White House — prompting Trump to promise her that there was no way he could beat Hillary Clinton.

The first lady’s office issued a statement calling the book “a work of fiction … that peddles false statements and total fabrications about Mrs. Trump.”

“Perhaps one day she will tell her own truthful story, but until then Mrs. Trump is focused on her role as first lady,” it said.

Trump has slammed Wolff and the book on Twitter, and the White House has called it “trash” and “full of lies,” among other things.

“Well, now that collusion with Russia is proving to be a total hoax and the only collusion is with Hillary Clinton and the FBI/Russia, the Fake News Media (Mainstream) and this phony new book are hitting out at every new front imaginable. They should try winning an election. Sad!” the president wrote Friday morning, a day after threatening legal action against Wolff and his publisher.

Wolff defended the book and his reporting on the “Today” show.

“My credibility is being questioned by a man who has less credibility than perhaps anyone who has ever walked on Earth at this point,” he snarked.