In fairness I think both sides qualify for that status. Politics in this country have become so extreme left and right that there's no real progress possible anymore.
Dictionary definition of a cult.
"A group of people having beliefs or practices regarded by others as strange or sinister, or as exercising excessive control over members."
It fits for both parties...
1) Extreme views.
2) Zero tolerance or consideration of other positions, and refusing that those other positions might have some relevance or correctness.
3) Absolute control by leadership.
4) Severe repercussions such as excommunication, coercion, and punishment for dissidence or not following the party norms.
The left and the right all have these elements in spades.