Yes other groups can represent a threat, but again it comes down to priorities and not always where you think you stand. Some might say you don't see BLM as a threat because you aren't 100% White, No I don't see BLM as a threat because they don't have the numbers, they don't have the organization, and they are specifically in their charters directed at the Justice system as it relates to police and courts.
Antifa aren't a threat because as rightly been pointed out thus far, all we have seen are basically what some can barely associate with Antifa, often described as Skinny Jean wearing latte sipping Anarchist.
Well if you really need to explained why that isn't a threat or more importantly how they lack the same organization and numbers then you really have no idea what you are talking about in terms of assessing a threat.
Alt-RIght are White Supramacist Neo Nazi's despite what they say, which is a marriage between the Aryan Brotherhood, the KKK, the Sons of Odin, and Hammer Skins which is a Prison gang.