> It doesn’t fully explain why Congress has allowed the expansion of executive power for nearly a century, resulting in more and more major issues being pushed to the Supreme Court.

It's because the US is a presidential republic with no concept of a non-confidence vote. This makes the sitting head of the party ~impossible to remove, and when government fails to reach consensus, instead of... Having an election, and let the voters decide, power de-facto ends up in the hands of the executive.