Krugman has this to say about it:
For those not familiar with how financial markets work, US Treasuries are the ultimate safe asset, used as collateral for everything. Even a hint that some Treasuries might not be honored could bring everything to a screeching halt
Musk and Trump are both in the habit of stiffing people they owe money. If markets even suspect that this habit will extend to Treasuries, God help us
It seems like Elon is controlling Trump even in this. Isn’t devaluing to swing markets an Elon move? He probably wants to sell a bunch of stock and simply trying to crash the EV market wasn’t enough if a wave for him to become the first trillionaire. Crashing the dollar it is I guess?