Mudslinging means attacking or criticizing someone by spreading negative and often false information about them, especially in politics or public discussions. Full definition
Mike O'Brien has been accused of mudslinging over claims that Michael Howard was indifferent to the needs of British Muslims. (politics.co.uk)
That left May as the main hope for Remain MPs, although her detached attitude during the campaign and her refusal to become involved in mudslinging have helped her to appeal to some Leavers as a unity figure. (theconversation.com)
RM: This is a naked piece of political mudslinging as Hammond spends several minutes extolling the greatness of the mansion that inspired Jane Austen's Pemberley in Pride and Prejudice, which he claims was threatened by opencast mining nearby that was authorised by a previous Labour government. (theguardian.com)