Real Dictionary

mudslinging
uncountable noun: If you accuse someone of mudslinging, you are accusing them of making insulting, unfair, and damaging remarks about their opponents.

mudslinging in American English
the practice of making unscrupulous, malicious attacks against an opponent, as in a political campaign
noun: an attempt to discredit one's competitor, opponent, etc., by malicious or scandalous attacks

mudslinging in British English
noun: casting malicious slurs on an opponent, esp in politics