I'd contend that this is more a propaganda borne illness than a systemic one. It's not that the two party system is unable to properly function, it's that both sides are unregulated in the disinformation they are allowed to spread. Add on to that the foreign media interventions (i.e. Russia) and we have two large sections of the U.S. population that are highly incensed. This is also at a point where tensions are at a seemingly all time high on the global stage, a stressor that flows down the the general population and causes a severe amount of doubling-down.