Why Republi[con]? Partially out of laziness, I got tired of having to type out the full name all the time and there is no real shorthand for them like “Dems” or “Libs” so now they can be referred to as “Cons” as in conservatives, con artists, con men, conspiracists.
Then there is the matter of the “Democrat Party” epithet which goes back to the days of Joseph McCarthy and his cronies in the 1950s and Barry Goldwater in the 1960s but it fell out of favor after McCarthy was exposed for the liar and demagogue that he was, and after Goldwater lost in a landslide to LBJ. It was resurrected by Newt Gingrich in the late 1980s, and was then picked up in the 1990s by such reactionary luminaries as Rush Limbaugh and Sean Hannity. Then in 2017, after becoming president, Trump started using the term, I’m assuming he was told by one of his toadies, most likely Steven Miller, that it was an insult, an “own the Libs” thing, he then gleefully started using it every chance he got. Although the epithet had been around before Trump it wasn’t until Trump started using it that its use became de rigueur amongst the faithful. And the press, out of ignorance or just plain laziness, just quotes them with no correcting or without any acknowledgment of the epithet’s history or meaning. I’m not objecting to the term’s use for any partisan pro-Democratic reason, quite the opposite, the objection is to its historically sordid use by anti-democratic reactionaries.