this is a question for those who know the inner workings of brokerages and margin accounts. when a broker offers a margin account, do they actually have a pool of money from which the client draws from? and if so, can this pool potentially be exhausted at any time, denying the client leverage? if there is indeed a pool of money that does decrease with use, then it seems to me that brokers who offer 100:1 margin rates could potentially be in danger of exhausting their available funds, thereby having to deny clients from borrowing money. is this really how a margin account works, or does it work differently? thanks!