Expect more shocks to the economy in the wake of the recent S&P downgrade to America's debt.

A Merrill Lynch economist, Ethan Harris, wrote in a recent report that if Congress' deficit "super committee" does not come up with tax and entitlement reforms later this year, there's a chance that S&P could downgrade the natiional rating another notch to AA.

Both Moody's and Fitch, the nation's other two major ratings agencies, could be expected to issue their first downgrades, according to Harris. "Unfortunately the initial reaction from Washington has been one of finger-pointing and questioning S&P decision and methodology. This implies that policy makers will not use this as a wake-up call to put a long-term deficit plan in place," Harris said.