If the fiscal cliff occurs, I don't think the Federal Reserve has the tools to offset that event.
The failure of Lehman Brothers demonstrated that liquidity provision by the Federal Reserve would not be sufficient to stop the crisis; substantial fiscal resources were necessary.
Monetary policy has less room to maneuver when interest rates are close to zero, while expansionary fiscal policy is likely both more effective and less costly in terms of increased debt burden when interest rates are pinned at low levels.
The greatest single cause of the fiscal surplus of the 1990s was the stock market bubble, which led to an unsustainably high level of economic activity and tax revenues.