I noticed that and bought some SWVXX recently That's a really nice yield for a money market fund. At Schwab are they treating the amount of cash in the money market as buying power. It looks like at A-Trade, they are not. That's in a cash account at least, not a margin account.
I have seen lots of $1 stocks with strong earnings and solid balance sheets triple, quadruple and more, but I have yet to see one go below zero.