And who sets the formula, who lobbies for laws to be passed to require it, who runs and owns the clearing houses? Hint: It's in the thread you linked.

> RH offered to open up stock market investing more broadly. They succeeded, clearly. But the regulations didn't change - there are still pro-Wall St, pro-incumbent rules and capital requirements. It's one of the most highly regulated industries in our nation. [0]

> So @aoc is right to ask how it can be that Robinhood stopped its clients from buying certain securities. And what she'll find is that the reason is that Dodd-Frank requires brokers like RH to post collateral to cover their clients' trading risk pre-settlement. [1]

> And it isn't the Fed or SEC who sets the rules. It's the Wall St owned central clearing entity itself, DTCC, that makes its own rules. So when the retail masses decided to squeeze the short-sellers, in the middle of crushing them, it was govt regulations which tripped them up. [2]

This last tweet in the thread was made about 13h ago, about a day after the previous last tweet in the thread. It's quite interesting, if you ask me.

> Update: the plot thickens ... @The_DTCC may have exercised its right to add additional margin charges for a set of these stocks. It's a Margin Liquidity Adjustment Charge. [3]

[0] https://twitter.com/KralcTrebor/status/1354952710202814470

[1] https://twitter.com/KralcTrebor/status/1354952711217807364

[2] https://twitter.com/KralcTrebor/status/1354952712400601099

[3] https://twitter.com/KralcTrebor/status/1355175395642003456