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) Last week the nation witnessed a courtroom spectacle that included the president's former personal lawyer and "fixer," Michael Cohen, groveling for mercy at a sentencing hearing while his daughter watched, a crutch at her side. Future historians might view the maudlin scene as the beginning of the end of the Trump presidency.

Paul Callan

The circumstances surrounding Cohen's guilty pleas suggest that special counsel Robert Mueller and Southern District of New York federal prosecutors believe Cohen and Trump broke the law in paying hush money to former Playboy model Karen McDougal and porn star Stephanie Clifford, aka Stormy Daniels. The clear purpose was to protect the president's reputation as a political candidate.

It is even possible that the president already has been indicted by a federal grand jury in a secret, sealed indictment that will be revealed only when he leaves the presidency. Of course, this is necessarily speculative, as prosecutors seal indictments to keep them secret.

Prosecutors generally use sealed indictments in three situations. The first is when they fear a suspect, upon hearing of his indictment, might destroy evidence before his arrest. The second is when they fear the suspect might flee. Neither of those applies to Trump. Even though he has the use of two well-equipped planes (Air Force One & Trump Force One), he is unlikely to flee the US and has no place to hide. But the third reason could be a factor: when the statute of limitations might expire before the suspect can be arraigned on the indictment.

Mueller and the New York Southern District prosecutors are bound by a Justice Department policy against indicting a sitting president.

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