We don't trade favors for the advancement of individual or party political objectives. For example, trading prisoners happens. Negotiating to have the prisoners held until after the election so your opponent loses is treason, whether done by a sitting president or a candidate.
Good luck with the prosecution.
So, your argument
now is "if we can get away with it, then it is okay to do it."
The prosecution of it will be easy when Trump is out of office. While in office, impeachment and then a Senate trial are the ways to go - and that they seem to be doing.
Mulvaney's words were offensive to plenty of Republican senators and House members, Kid, even if you think it's a nothingburger.