Actually the tax law does not bar rabbanim or other clergy from endorsing candidates per se. That would be a violation of the Free Speech clause. It bars them from doing so in the names of their institutions or from their pulpits.
BTW, being that we are correcting spelling and grammar, the title of this thread should end “for whom” . According to grammarly.com
“Whom should be used to refer to the object of a verb or preposition. When in doubt, try this simple trick: If you can replace the word with ‘he’ or ‘’she’, use ‘who’. If you can replace it with ‘him’ or ‘her’, use ‘whom’.”