I recall that Sen Mendendez criticized Obama on Iran? Maybe voted against an Iran deal?
Obama sicced the DOJ on him for accepting campaign cash in exchange for favors for a sleazy donor.
That is almost impossible to prove in the US unless you have a quid pro quo promise on audio.
That never happens. Doing the favor after receiving the cash is not enough under US law.
He was found not guilty. The Senator seemed normal to me. The donor was a real POS.