Paul Callan is a CNN legal analyst, a former New York homicide prosecutor and current counsel at the New York law firm of Edelman & Edelman PC , focusing on wrongful conviction and civil rights cases. Follow him on Twitter @paulcallan . The opinions expressed in this commentary are his own.

(CNN) It's becoming increasingly clear who President Donald Trump really wants to represent him in the Robert Mueller investigation -- and there's a good reason he can't have him.

When John Dowd quit this week as lead counsel on Trump's legal team and the President made an effort to recruit "deep state" conspiracy theorist and conservative legal commentator Joseph diGenova to the team , the conclusion could only be that Trump wants to go to war against Mueller, using the tactics favored by his onetime mentor Roy Cohn.

In effect, the President wants to wage an aggressive, and probably dirty war, on the special counsel. Cohn, having died in 1986, isn't available. But there may be other lawyers who can fill that role.

In the early years of his Manhattan real estate career, Trump was a protégé of Cohn's who had gained fame decades earlier as counsel to the notorious McCarthy committee in the 1950s.

According to the Times, Trump even said , "Where's my Roy Cohn?" last year when Attorney General Jeff Sessions recused himself from the Russia investigation, helping eventually to open the door for the appointment of a special counsel.

There are no reports of Trump threatening anyone with photos of the lead attorneys on his current legal defense team, which until Thursday included Dowd and the handlebar-mustachioed Ty Cobb. The public posture of the defense team in recent months suggests these lawyers have counseled patience and measured cooperation with the Mueller investigation in the belief that any other tactic would make the President look guilty in the eyes of Mueller and the public.

The tactic also reflects the pragmatic assessment that Mueller has the subpoena power of a federal grand jury empowering him to get anything legally relevant to the Russia election interference probe and has been authorized in writing by Deputy Attorney General Rod Rosenstein to pursue "any matters that arose or may arise directly from the investigation."

The President may well be disturbed by the special counsel's most recent subpoena of the Trump Organization and its potential to cross his red line, opening for investigational scrutiny any potential secrets of his business (and perhaps even Trump's tax returns).

The shake-up on Trump's legal team is likely to continue, as indicated by the discussion of adding diGenova to the team. Whether DiGenova or his wife, Victoria Toensing, survive the White House vetting process remains to be seen . Beyond the usual background checks, the President's personal assessment about how they look on television, more specifically on Fox News television, undoubtedly will be part of the process.

One thing is crystal clear. New recruits to the legal team will have to be hard-edged conservatives who are aggressive fighters in the Cohn mode if they expect to fill the seats vacated by Dowd and other defense team members as Trump reshapes his legal strategy.

The re-emergence of hard-liners such as Michael Cohen and Marc Kasowitz, who continue to advise the President from the shadows despite controversial actions both lawyers have taken in the past, also suggests that a new and tougher defense strategy is in the works.

She was Cohen attempted to purchase the silence of porn star Stormy Daniels with his own money and was also allegedly involved in the "catch and kill" agreement used to silence former Playboy Playmate Karen McDougal. (Cohen says he has no recollection of communications regarding McDougal and her agreement with the National Enquirer's parent company, American Media Inc.)She was interviewed Thursday by CNN's Anderson Cooper about an alleged 10-month affair with the President. Both women say they had sexual relationships with Trump while he was married to Melania Trump. Representatives for the President have denied there were such affairs.

Kasowitz had largely disappeared from the public view after his last controversial attack on an individual who dared to criticize him in an email.

Kasowitz replied via emails that threatened: "I'm on you now. You are f-----g with me now Let's see who you are Watch your back, b---h," .... "Call me. Don't be afraid, you piece of s---. Stand up. If you don't call, you're just afraid." .... "I already know where you live, I'm on you. You might as well call me. You will see me. I promise. Bro. ..."

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Through the years Kasowitz has represented Trump using scorched earth legal tactics in a host of contentious cases, including Trump's divorce proceedings, bankruptcy proceedings, the Trump University litigation as well as accusations that Trump engaged in inappropriate sexual contact with a number of women. Trump has denied all of these claims.

The signs are clear. While the White House has repeatedly said there are no plans to fire Mueller, Trump is shifting to an aggressive legal defense strategy, and the departure of Dowd portends more shake-ups in the legal team.

Watch for forceful attacks on Mueller, including calls for his dismissal, shake-ups at the Justice Department and FBI as well as presidential noncooperation with the Mueller probe. The ghost of Roy Cohn is in the air, but perhaps Trump should be careful. By the time of his death, Cohn had been disbarred for dishonesty and his career shattered.

A better spirit to invoke might be that of Richard Nixon, who learned that going to war with a special prosecutor is the path to resignation and disgrace rather than vindication.