When someone charges they move quickly (sometimes violently) and often carelessly.
He began running through the room and charged directly into a table!
To charge off is to charge away.
I told her to stop shouting and she charged off.
A careless person may fall off a cliff, or a person commiting suicide may jump off a cliff. Regardless of whatever action causes someone to go over the edge of a cliff, it can undoubtedly be considered a bad situation. That is the important thing to bear in mind when considering the meaning of off the cliff in this sentence.
The general meaning of an economy charging off a cliff is an economy which is on the path to destruction.
If the U.S. Congress is going to get a second crack at rescuing an economy charging off a cliff...
The above clause can be paraphrased as:
If the U.S. Congress is going to get a second crack at rescuing an economy heading into serious trouble...
I am not a teacher.