Yes - when the housing market went south and foreclosures started piling up, the holders of these securities couldn't value them, as the mortgages had been sliced and diced so much in the process of turning them into securities. So now, nobody wants to take the risk of buying them - they have a market value of zero, even though the underlying value may be okay.
This Week: George Will is the panel member who is most critical of John McCain, although Sam Donaldson thinks that McCain needs to be more moderate and not lose his temper. Maybe George Will needs to go back to his bow-tie and reduce the circulation a little.