It mainly morphed into the Tea Party, which was also a reaction to a black man being President as well as being an astroturf job by the Kochs.
Many Republicans especially at grassroots level still hold to pre-millenial dispensationalism and a lot were convinced Obama was the antichrist they'd been waitng for.
This shit ties into other shit about Satanic cabals and the NWO and black helicopters, 9/11 truthers, the rapture and FEMA death camps, plus false flag school shootings, race wars and apocalyptic battles in Israel. All of this is fairly mainstream within the GOP now, but it doesn't get picked up because, as with ISIS own apocalyptic millennial theology, it seems so self-evidently stupid and insane a lot of the MSM don't buy that anyone could honestly believe it, yet these beliefs are central to a lot of modern Republicanism.
On top of this lunacy you have the Trump types who deliberately stoke these fires to bolster support for their hellacious dreams of a dog eat dog capitalist authoritarian society. Climate change is a myth and more nukes iz gud. This has a good chance of tipping the species closer to the brink so a lot of Reps are all for it.
The comparison with ISIS isn't a glib one, altho I'd argue the GOP is far more extremist and dangerous purely because they have a mandate and a nuclear arsenal.