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'.
(..) Alert. Alert. HAL: But they didn't call him Unrelenting for nothing. Ship, release new probes. I want them to map every square klick of this mud ball... ...and set charges to force that son of a cur into the open. If Bolphunga couldn't find Mogo directly, then he'd find him indirectly: (..)2011 Green Lantern: Emerald Knights