Well, there is nothing that can prevent a bank run: at times of crisis when bank would suffer a bank run, when trust in currency is lost, government can only pr

Well, there is nothing that can prevent a bank run: at times of crisis when bank would suffer a bank run, when trust in currency is lost, government can only print out more money, thus deflating the value of a dollar. Which is when people will still want to convert to something that is better guaranteed to preserve value: prompting a bank run! US has so far resisted this because it's such a huge economy that nobody wants to see default on its debts (all foreign debt it has is denominated in USD), and as dollar drops, everybody starts buying in the US.