He was able to lead an effective administration despite diminishing capabilities because he assembled a highly qualified team and leveraged the bureaucracy. So while it was far from ideal, it managed fairly well.

Trump is an autocrat surrounded by mostly utterly unqualified yes men and women who view the existing bureaucracy and its expertise as the enemy. So his obvious significant and advancing mental and physical deterioration has far more serious consequences. There are no guardrails or support structures in place.