I say let the conservatives come up with their own denigrating term.
Sure, Fox has her on in an attempt to damage Democrats, but I doubt
it does much harm. How many Fox viewers would vote Democratic anyway?
Conservatives have come up with their own denigrating term for those that lean left; it is the term LIBERAL and the media has mostly bought into this as well. Note that polling data supports this since the data shows that while there are more members of the Dem party than GOP party more people wish to define themselves as conservative than liberal. That means that there are Dems that do NOT wish to label themselves as liberal because liberal has the sigma of being 'far left'. (and progressive is even more radical as far as the mainstream media is concerned).
As for Waters and what Fox is doing; Fox has people like Waters on to show that Trump isn't so out-there as the so called mainstream media (really mostly just CNN), is implying. It isn't to get GOP viewers to vote for Dems (DUH!) but instead to get GOP viewers to continue to support Trump as the lesser of the evils between conservatives and liberals.