mud-slinging 
noun [mass noun] informal
The use of insults and accusations, especially unjust ones, with the aim of damaging the reputation of an opponent: politicians seem to rely on mud-slinging instead of argument...
- It makes me angry that the leader of the opposition, behind his endless accusations and mud-slinging at the PM, seems to be a very lazy and unimaginative individual.
- The Polish deal was marked by mud-slinging, with accusation and counter-accusation from both sides, although none has yet stuck.
- This scathing assessment of the ruling meant that critics would have to find solid arguments to attack his work, rather than rely on mud-slinging, Mr Lomborg said.
Derivatives
mud-sling
- ‘Instead of the Irish Government responding to the demands and ending their support, they have instead chosen to mud-sling against the anti-war movement and tell lies about it,’ he said.
- Is the ability to mud-sling the most desired talent for our next President?
- I was just pointing out your flawed logic, but yet again you'd rather mud-sling than make actual logical points or counterarguments.
mud-slinger
- Like most anti-war mud-slingers, he merely sets-up a string of false straw-men & then - surprise, surprise - manages to knock them all down.
- Plus, she's a bare-knuckled, gritty mud-slinger that would give him a worthwhile opponent when the debates roll around.
- I was wondering why he's being such a mud-slinger, you know, against Al Gore.