How would you define "third party" in this case? We now know that the assassin was a follower of Nick Fuentes, acting on the suggestion of Laura Loomer. Both are working with Donald Trump on destabilizing the US. On top of that, the victim itself was also a seditious actor trying to destabilize the US.

In that light, does it really matter what tier party the assassin belonged to? The joint common enemy you allude to is already inside the white house, and as long as that is still up for debate, the country has no future.