What Is A, 'Cuck?'

From Wikipedia.

"Cuckservative" is a neologistic epithet formed as a portmanteau of the word cuckold and the political designation conservative. It has become an increasingly popular pejorative label used among alt-right supporters 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 political rise of Donald Trump and his 2016 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.