There are so many things going on right now it is hard to isolate the variables.
Interestingly, the credit market has not seized up. It has tightened and it needed to do it.
The largest micro variable in play right now is the prospect of the capital gains tax rate doubling after Obama takes office. He said he was going to do it and investors believe him.
There is/was a lot of investors holding onto stock assets that have/had large unrealized gains. Yep, even with the market tanking the way it is now, it is still higher than it was 15 years ago.
People who are/were sitting on those gains are/have elected to realize those gains under the current tax structure. They do that by selling those assets. There is no 30 day waiting period needed to buy them back, so theoretically you would expect the buy/sell volume to wash out. But, many of these investors are waiting to see what happens over the next few weeks. There is no urgency in buying them back.
If PE BO would simply announce he will not raise taxes while the country is in this financial trouble, the stock market would stabilize and rally immediately. This is the number one thing suppressing the short term market now.