Where in the Constitution does it say that the federal government is obligated to bail out failing banks?

[Spock (rhp)]

there is no such requirement in the Constitution.

there is the "general welfare" clause which permits Congress to take such action as it deems fit to promote the general welfare, unless specifically prohibited elsewhere in the Constitution.

note that Congress is not required to act by the general welfare clause, only permitted to do so.

there is a long argument about the side effects on people's motivations if you give them free goods and services which suggests that the welfare clause shouldn't be used to provide for things that the people are capable of providing for themselves -- government provided health care would have been laughed out of the tavern back in 1790, for example.