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
This could trigger a Minsky moment. And a world wide financial meltdown. Then he’ll just say haha just kidding. Once that genie is out of the bottle though, there’s no going back.
Elon won’t say anything until Minsky starts to screw him over