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 those of the author. View more opinion articles on CNN.

(CNN) If Michael Cohen can show federal prosecutors credible evidence that President Donald Trump knew in advance about the infamous Trump Tower Russia meeting of June 9, 2016 -- as Cohen now reportedly claims -- the President's son could be facing perjury charges.

It was Donald Jr. who approved the time, location and participants in a meeting that included a Russian lawyer, Natalia Veselnitskaya, and a Russian-American lobbyist, Rinat Akhmetshin. He also brought to the Trump Tower conference table the then-chairman of Trump's campaign, Paul Manafort, and brother-in-law Jared Kushner among others.

The President has repeatedly denied being told about the meeting before it happened. He has said this to the press and the public, most recently on Friday via Twitter , but apparently never to federal investigators or under oath. Under the circumstances, if Cohen's claim is corroborated -- a big "if" -- this may be a reprehensible lie, but it's not necessarily criminal. Still, it is so serious that it could theoretically give special counsel Robert Mueller the leverage to propose a deal: Resign the presidency in exchange for immunity for Don Jr. Otherwise Don Jr. will be indicted for lying to the Senate Judiciary Committee, and could -- again, theoretically -- go to jail.

JUST WATCHED Attorney-Client privilege and the Cohen tape Replay More Videos ... MUST WATCH Attorney-Client privilege and the Cohen tape 06:13

Patrick Davis, deputy chief investigative counsel: "Did you inform your father about the meeting or the underlying offer prior to the meeting?"

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