"widely believed"? Believed by whom and why? Dodd-Frank is not a secret. There either is a requirement in Dodd-Frank act or not. If there is, you or the persons believing it could just quote the relevant text.

According to Vlad from Robinhood, as said in Clubhouse interview with E. Musk, there is discretionary (i.e. arbitrary) part of the collateral requirement set by NSCC.

Initially NSCC asked RH for $3 billion in collateral which RH didn't have and they managed to negotiate it down to $700 million, which they did have.

Which begs the question: if $3 billion was required by Dodd-Frank, then did NSCC commit securities fraud by agreeing to lower it to $700 million?

And if $700 million was enough to satisfy Dodd-Frank, then why did they ask for $3 billion initially?

And what if $500 would be enough? Or $200 million?

Or maybe Dodd-Frank doesn't dictate collateral requirements on an individual stock at all?