The candidates started 'slinging mud' (at each other) early in the campaign.
His shoes were covered with 'mud'. = His shoes were caked in/with 'mud'.
The scandal ruined his reputation and now 'his name is mud'.
(..) and see if there's any accidents, or road closings. It was raining like a son of a bitch here last night. They're probably just stuck in the mud someplace. Otis: Shut your mouthi I said, shut your fucking mouth! Listen, you Malibu middleclass Barbie piece of shit, (..)2003 House of 1000 Corpses