Richard Nixon Biographer: Hillary Clinton Has 'Nixonian Attributes'

What the 2016 Democratic candidate and the 37th president have in common.

“Mrs. Clinton does have some Nixonian attributes. She can be guarded and defensive, a little bit too tough on her enemies,” Thomas said in ABC News' “Power Players” series. “I saw this firsthand. She needs to watch that.”

“She’s not involved in anything like Watergate. She's not Nixon,” he continued. “If you think you can manipulate the press and stonewall forever, [when] you're running for president and you're president, I don't think that works.”

Thomas’ book, “Being Nixon: A Man Divided,” captures the contradictions of the 37th president, a profane and often bitter man who was also an optimist (he always thought even bad movies would get better, Thomas writes) who won four elections on national tickets.

Thomas describes Nixon’s habit of working out of the Executive Office Building on the White House conflict -- he didn’t like the Oval Office -- in overnight hours, when he couldn’t sleep.

“Here's the guy who's the most powerful political person in the universe at the time -- didn't like people. He was shy,” Thomas said. “Mostly he wanted to be alone.”

The Nixon that comes through on the famous Watergate tapes -- vindictive, racist, anti-Semitic, angry -- doesn’t capture the full man, he said.

Hillary Clinton’s representatives declined comment when reached by ABC News.

ABC News' Ali Dukakis and Tom Thornton contributed to this report.