Cohen’s plea language states that he was “directed” to make the payments by an unnamed presidential candidate.
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?
P.S. — Imagine how simple Trump’s defense could be if this goes anywhere: “Yes, I directed him to make the payments. He was my lawyer, and he advised me it was perfectly legal!”