Comment by treis

It's impossible for both things to be true. For the dollar to be the reserve currency countries need to accumulate dollars. They can't do that unless more dollars leave the US than come back.

The problem is that countries don't just take the dollars and sit on them. We're on the third iteration of solving this intractable problem:

Try 1 was gold. The US was running out of gold and Nixon had to end redemption of dollars for gold.

Try 2 was assets (think the Japanese buying everything in the 80s). That was unpopular and the Plaza Accords put an end to it with significant damage to the Japanese economy

Try 3 is government debt. But it's the same fundamental problem. The US isn't ever willingly going to give back assets for this debt. Everyone agrees with the polite fiction that the US will and so things are fine. But if they ever expect actual stuff for that debt it will all break down again.