As long as hes still around hes a threat cause hes got a really weirdly large number of people in his cult. It would be folly to assume the republican party is down and out. Without trump they will be headless for awhile, but they have a very easy time rallying a fear based... base. And don't forget, even with all the shit he pulled and how incompetent he is and his horrendous response to covid, he still got the second highest number of votes. That isn't even taking into account the electoral college which makes pure numbers less important then where the votes are, and a good number of important electoral states are pretty red.
Not to mention he and his ilk entrenched a terrifying number of people into positions of legal power, like the Supreme Court, and other courts, that have been quietly, and steadily shifting the balance of power even more into their favor, by passing laws that are blatantly conservative in nature, with partisan agendas all over them.
They are a religious cult, that has been groomed for decades, to view themselves as the chosen of their diety, that their views on the world are not only "true american" but also religiously endorsed, and that anyone that is against them are evil enemies of the country at best, and literal minions of satan at worst. They've fused their jingoism and their faith into a single entity, so attacking one is attacking the other in their eyes.
They've been taught that any actions are justified in defense of their faith and their idea of what the country should be, and they are GLEEFULLY willing to demonstrate that, and even live stream it, like they did on 1/6. They've been taught that to question their ordained leaders is blasphemy, and zealously turn on anyone that doesn't follow their agreed upon party line, including threatening them with death.
So yeah, they are hardly irrelevant.