The idea of "powerful" is complex and sophisticated. In today's global situation - power is both soft (influence, economic power, building alliances and dependencies) and hard (military, threat of force).

It is also crucial to know what government debt means on a macroeconomic level rather than trying to gain an intuition of it through personal debt. Although it sounds the same "borrow and pay back", the nature and how debt works at a national level versus personal level is not even vaguely comparable.

None of this is really even approachable as an entire topic in a reddit post. Suffice to say that if there is a default on national debt, a nation loses soft power very quickly. A large part of the notion that the US is powerful is the fact that other countries/people want to hold US debt because it is safe and the US is seen as a reliable economic power. The US has used this power to build a global economic order consisting of trade. Threatening the functioning of this order diminishes the US significantly and defaulting on US debt is a very sure way of destabilizing the global order.