There is no single root cause in a complex system of checks and balances. Many parts need to fail for things to get as bad as they are now. Trying to reduce everything to a single fault is either stupid populism or blatant propaganda.

IMHO the highest court, which is tasked with delivering timely justice, ought to make their decisions in a reasonable amount of time, and not allow legally questionable executive actions to continue while the legal question is unanswered.

You may consider that populist, but my opinion is that SCOTUS has derelicted their constitutional duty in these trying times.