Earlier quoted context omitted.
Sure, but basically every currency has some theoretical problem. Usually it's just about the currency becoming worthless (usually only a problem in government controlled currencies that have loans in foreign currencies), or people just not accepting it anymore. There's no inherent value in any currency, it's just a useful fiction because it's really hard to go get five goats to trade somebody for a laptop.
Currencies are propped up by taxes. The IRS wants a significant percentage of the US GDP paid in USD, as long as the economy exists and the government doesn’t print truly vast amounts of money from thin air the USD can only move within a fairly narrow range.
Given the number of countries using the dollar as their reserve currency, value could collapse quite a ways without the US doing anything.
It's not likely, but neither is a 50 + 1 attack on bitcoin given the amount of computing power currently tied up there.