Michael D'Antonio is the author of the book " Never Enough: Donald Trump and the Pursuit of Success " (St. Martin's Press). The opinions expressed in this commentary are his.

(CNN) Though many individuals likely contributed to the President's decision to fire FBI Director James Comey, one notable one may have been Roger Stone, a 64-year-old close friend of Donald Trump and central figure in the FBI investigation into Trump campaign ties to Russia.

In the middle of the Watergate scandal, Stone, who engaged in dirty tricks during Richard Nixon's 1972 campaign, was discovered to have hired a Republican operative to infiltrate the George McGovern campaign and was subsequently fired from his job. After the President's resignation, Stone remained an ardent Nixon apologist and loyalist. He even had the man's face tattooed on his back and devoted his life to ruthless, anything-goes politics (or political consulting, as you may know it). Stone's motto was and continues to be: "Admit nothing, deny everything, launch counterattack." And anyone who has watched Trump closely over the years would think it was his personal slogan, too.

Stone was introduced to Trump in the 1980s by the notorious Roy Cohn. Then a Manhattan lawyer who represented several reputed mobsters, Cohn had become infamous in the 1950s as the chief inquisitor during Joe McCarthy's "Red Scare" hearings in the United States Senate. After McCarthy's inquisition was shut down, Cohn began a new life as a political and legal fixer. He became a mentor to Stone and Trump and taught both men how to manipulate the media and bully opponents. After he died, they carried on in his spirit.

In Cohn's absence, Stone became Trump's main adviser for many political efforts, beginning with a flirtation with a run for the White House in 1987 (Trump even gave a speech in New Hampshire). But as much as Trump may have appreciated Stone's extreme pugnaciousness, he also had his reservations. Stone traffics in conspiracy theories and misogyny (see his disgraceful comments about Hillary Clinton) and has repeatedly suggested that leading political figures should be killed or kill themselves.

In 2015, Trump called Stone a " loser " and made a show of separating himself from him. Then, in the spring of 2016, Trump seemed to embrace him again. "Roger is never too far away from Trump," a source told Dylan Byers of CNN Politics. "He's always talking to Donald." Yet another source said, "Roger and Trump always wind up finding their way back to each other."

In the White House, Trump has continued to answer calls from old friends, and Stone seems to be among them. Days ago, the DailyCaller published a story with the headline, "Roger Stone still talks with President Trump." Reporter Kerry Picket wrote, "Republican political operative Roger Stone says he still communicates with President Donald Trump, and the last conversation he had was relatively recent."

Both CNN and Politico are now reporting that Stone has been among those urging Trump to fire Comey. And the President's longtime friend would have reason to want Comey fired. Stone is at the center of the controversy over Russia's attempt to influence the 2016 election -- after tweeting a message that predicted trouble for Clinton campaign official John Podesta, whose hacked emails were then published by WikiLeaks. Stone also hinted at an "October surprise" that would be devastating to Clinton and said he had communicated with WikiLeaks founder Julian Assange.

More recently, as he was subject to more scrutiny, Stone called the FBI probe into his activities " a witch hunt ." In taking on the FBI directly, Stone employed his longstanding strategy of always staying on the offensive. Operatives who use this method view every conflict as a matter of survival, which justifies the use of any weapon that might be at hand. Thus, an opponent can be labeled a criminal, and crowds can be exhorted with chants of "lock her up." No tactic is too low if you are fighting for your life.

Trump has adopted a similar approach to dealing with those who oppose him. His violent rhetoric about protesters -- "I'd like to punch him in the face" -- at his campaign stops and his indulgence of conspiracy theorists like Alex Jones of InfoWars, a radical right-wing radio show host, showed that he, too, was comfortable doing whatever was required to get what he wanted.

In addition to their aggression, Trump and Stone also share a preference for defying convention. One reliable way to do this involves making statements that are too shocking to believe. Thus, we have Stone responding to Comey's firing with the comment it's " about time " and then Trump taking to Twitter to say, "Have not spoken to Roger in a long time -- had nothing to do with my decision." Stone later took to Twitter as well, saying that while he hadn't "urged" the President to dismiss Comey, he supported his decision "100%."

Understanding this ruthless Stone/Trump approach makes it easier to recognize what may have happened with Comey. Since the FBI investigation into Trump campaign ties to Russia was hitting close to home, both Trump and Stone stood to benefit from Comey's dismissal. And given their 30-year history of working together to further their objectives by any means necessary, this decision fits well within an existing paradigm.

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With Comey's firing, we now have a new demonstration of the lengths to which these men will go to thwart their opponents. Under Stone's apparent influence, Trump has sacrificed the integrity of the presidency and thrown the nation into a political crisis that may eventually rival the one provoked by Nixon's abuse of presidential power. As CNN contributor Jeffrey Toobin noted, Stone subscribes to " Nixonian hardball ," which includes using what others consider unethical methods in order to win.

He and Trump have brought this style of play back to the White House.