[maest]

You should read the notes, they help answer your questions.

Anyway, 2 points:

1. This is not about margin accounts. When trading on margin, it's RH that's financing you and taking on the risk. That's separate from what the clearing house does. Incidentally, RH did increase margin requirements due to the higher volatility.

2. The problem is RH offers instant settlement. That is, you can use your proceeds from a trade immediately in the apo, before even the trade is settled. That exposes RH, and the clearing house to settlement failures, and that's true regardless if the trade was done on a margin account or not. And that's the risk that clearing houses try to mitigate via asking for collateral.

[gmethowaway]

How about Interactive Brokers case then, or AFAIK TD Ameritrade. They don't offer instant settlement (or may be they do, but the same was applied to settled money). They blocked buying GME stock on nonmargin accounts with settled money. What's the risk for them? I don't know if the same was applied to RH (blocking GME stock on non margin account with settled money) but what I read is RH even removed GME ticker from the search, so you can't buy it.

edit: from the Bloomberg article you posted: "The trouble on Thursday began around 10 a.m., when after days of turbulence, the DTCC demanded significantly more collateral from member brokers, according to two people familiar with the matter.". So I have my money settled in my broker's account for months, I'm buying without lending any additional money, why can't my broker show that I have all the collateral needed or even transfer my money? Am I missing something here? Does it work per broker and not per broker's account maybe? So people with settled cash are affected becasuse of other people doesn't have enough collateral? Or may be because showing/transferring collateral to DTCC is not instantenius?