He's quite right.
The more the US sanctions other countries (i.e. cuts itself off from world trade), the less incentive there is for foreigners to use/hold dollars.
Failure of the Iran deal may not cause the end of the dollar's hegemony, but it'll move the needle in that direction.
...I'm astounded that he actually said this in public.
In the long term, yes, by limiting the government's ability to finance itself by inflation.
But in the short term, the transition could be very painful, even catastrophic (no one really knows how low the dollar would fall absent this artificial foreign demand).
If the wrong kind of government's in power during the crisis (i.e. one that opposes the necessary structural changes), things could get much worse, not better.
See: Argentina
