Here's that iceberg that is drifting toward our economy's Titanic... and no, it ain't a virus, but it is our choice:
Years of easy credit, easy money. The pile of debt from Baa to lower ratings is the real threat here, for its sustainability is heavily contingent on two highly correlated factors: cost of debt (interest rates) and availability of liquidity. The two factors are closely correlated, but are also somewhat distinct. And both are linked to the state of the global economy.
There are additional problems hidden within A and even Aa rated debt, since these ratings are vulnerable to downgrades, and current Aa rating shifting to Baa or Ba will entail a discrete jump in the cost of debt refinancing and carry.