An ex-Secret Service officer's forthcoming book on Democratic presidential front-runner Hillary Clinton reportedly claims she has a “volcanic” leadership style and lacks the "temperament" to hold office -- the same charge the candidate leveled last week at Donald Trump.

The book, “Crisis of Character,” is due to be released June 28 – a month before Clinton is likely to take the stage to accept the Democratic presidential nomination in Philadelphia. Written by ex-Secret Service Officer Gary J. Byrne, who was “posted directly outside President Clinton’s Oval Office,” the 285-page book paints Clinton as disdainful of rules and erratic in her personality.

While some extracts have already been released on the Amazon.com preview page, the New York Post reported Monday that Byrne claims Clinton is too “erratic, uncontrollable and occasionally violent” to become commander-in-chief.

Byrne describes Clinton as switching quickly from friendly to angry in a moment, and repeatedly screaming obscenities at her husband, the Secret Service and White House staffers. Secret Service agents even had to consider what to do in case the first lady attacked the president physically, Byrne claims.

“Hillary Clinton is now poised to become the Democratic nominee for president of the United States, but she simply lacks the integrity and temperament to serve in the office,” Byrne wrote, according to the Post.

“From the bottom of my soul I know this to be true. And with Hillary’s latest rise, I realize that her own leadership style — volcanic, impulsive, enabled by sycophants, and disdainful of the rules set for everyone else — hasn’t changed a bit.”

Incidentally, Clinton last week accused presumptive Republican nominee Trump of being "temperamentally unfit" for office.

In the Amazon preview of the book, Byrne recalled an alleged fight between the first couple during the summer of 1995 in Chapter 1, “The Vase.” Byrne said a vase was smashed during the loud argument and the next morning President Clinton sported “a shiner, a real, put-a-steak-on-it black eye.” Clinton’s personal scheduler Nancy Hernreich allegedly told Byrne the eye condition was a result of Clinton’s allergy to coffee.

Clinton's critics say the book sheds light on the Clintons’ character and suitability for office.

"It’s about them having a separate set of rules or not having to follow the rules, and there are basic questions of character … in how they treated others and how they treated their colleagues,” Matt Schlapp, chairman of the American Conservative Union, said Monday on Fox News.

However, Democratic strategist Mary Anne Marsh, a former adviser to John Kerry, said it was an example of the negative 2016 campaign and would only play into the tactics of Trump.

"I think this book is just one more example of where this campaign is going, which is straight to the gutter,” Marsh said. “A really negative campaign is the bet Donald Trump is hoping for because it’s the only one he can win, because people get turned off by truly negative campaigns.”

The Clinton campaign dismissed the book, telling the Post it belongs in the fantasy section of a store.

“Gary Byrne joins the ranks of Ed Klein and other ‘authors’ in this latest in a long line of books attempting to cash in on the election cycle with their nonsense,” spokesman Nick Merrill said in a statement. “It should be put in the fantasy section of the book store.”

White House spokesman Josh Earnest wouldn’t be drawn into commenting directly about the book.

“I'd think I'd reserve judgment about the wisdom of writing a book from such a perspective until I know more about the book,” Earnest told reporters.