Paul Callan is a CNN legal analyst, a former New York homicide prosecutor and of counsel to 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. View more opinion on CNN.

(CNN) Michael Cohen's attorney, Lanny Davis, announced this month that his client had recently registered as a Democrat. But everyone knows what Michael Cohen really is. He is a lawyer -- and a rat.

And as a lawyer-rat he is a particularly loathsome member of the order Rodentia. This is because clients confide their most intimate secrets to lawyers thinking they are protected by the attorney-client privilege. When their trusted lawyer reveals his true identity as a member of the rat family who has peddled their secrets to save his own rodent skin, like Cohen did to President Donald Trump, their sense of betrayal is grave to say the least. Such conduct will soon cause the rat to discover he now has only two categories of friends -- exterminators and prosecutors. In both cases their affection for the hated rodent may be warranted.

Paul Callan

Prosecutors sometimes achieve courtroom success by relying on the testimony of rats. Special counsel Robert Mueller is always seeking their cooperation and offering them tasty "cooperation deals" for their information and testimony. Cohen has been scurrying between Mueller's office and the offices of New York state and federal prosecutors in compliance with a plea deal recently negotiated by New York federal prosecutors. Cohen, in an unusual display of sound judgment, has wisely elected to team up with the prosecutors rather than the exterminators.

He hopes to achieve not only a more lenient sentence but also some element of redemption by assisting federal prosecutors and acting as a "whistleblower" of sorts. While turncoats often spend less time in jail, they rarely get their reputations back, regardless of the value of their information. "Sammy the Bull" is still viewed as a mobster, and Cohen lacks the gravitas of John Dean, the former Nixon White House counsel who cooperated with prosecutors in the Watergate scandal and became the poster child of turncoat redemption.

As a rat, Cohen executed an unorthodox move. He announced, through his attorney, his decision to affiliate with the Democratic Party. We rarely associate rats with exercising the constitutional right to affiliate with a political party and vote because some are felons who are prohibited by law from voting.

Read More