The phrase "nasty party" is used to describe a political group or party that is considered mean, cruel, or unpleasant in their actions or policies. Full definition
This should be the basis of a newspaper article by one of our prominent politicians... I have often been frustrated at the fact that Cameron is never asked why he, nice clean Dave, joined the Tories when they were the nastiest of nasty parties. (nextleft.org)
Echoing Theresa May's famous soundbite, he added: «Labour is in danger of becoming the new nasty party if this behaviour continues unchecked.» (totalpolitics.com)