Wikipedia
Cuckservative is a neologistic epithet. It is a portmanteau of the word cuckold and the political designation conservative, and has become an increasingly popular pejorative label used within the conservative movement, and among white supremacists in the United States.
The word cuckservative reached a high level of mainstream political conversation around mid-July 2015, where it gained media attention just a few weeks before the start of the first Republican primary debate for the 2016 United States Presidential election. It has maintained its popularity, especially with the rise of Donald Trump and his presidential run.
The term originated on websites such as 4chan (specifically the /pol/ imageboard), the right-wing message board My Posting Career, the political and social blog The Right Stuff, and other sites in the alt-right movement.