This policy is more often known as "shoot yourself in the foot" as you stab your allies in the back and isolate yourself both at home and abroad.

American economy hangs by a thread, which is supported by countries like China, Japan and Saudi Arabia buying their debt. And these buyers don't seem so interested anymore. They'd much rather be selling it actually. So once they sell enough to cause default, who's gonna buy the dollar?

Oh and a euro reserve is impossible. The Euro is propped up by the ECB's frantic printing spree in hopes of getting people to open their wallets and buy useless shit that they don't need. It won't last for long.