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'.
(..) No, it's perfectly possible. It's just bloody difficult. Interesting. Because Arthur keeps telling me it can't be done. Hmm. Arthur. You still working with that stick in the mud? He is good at what he does, right? Oh, he's the best, but he has no imagination. Not like you. (..)2010 Inception