Dirty campaign stuff (3)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">dirty campaign stuff</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for mud that I've seen before include "Earth and water mixed" , "Soft wet earth" , "in your eye, it's an affable toast" , "damaging allegations" , "-, -, Glorious - (Flanders and Swann)" .)