Take it one step further ...
The only thing that made these payments an "illegal campaign contribution" by any interpretation was that they were made by Cohen, not Trump. So how does Cohen's admission have any bearing on Trump?
I think that would be up to the Federal Elections Commission to decide. If they were to make a criminal referral to the Justice Department. That’s highly speculative and extremely rare.
Of course if the Democrats take control of the House, it could be grounds for impeachment, an impeachment that would fail in the Senate. “High crimes and misdemeanors” are whatever the votes of at least 218 members of the House say they are.