Even though the case of mcculloch v. maryland was about the creation of a national bank, what was the fundamental idea that was being questioned in this case?

the financial future of all states
the economic stability of the state of maryland
the power held by state and federal governments

The fundamental idea that was being argued in this case is the:

“The power held by state and federal governments”

McCulloch v. Maryland, was a milestone decision by the Supreme Court of the United States. The state of Maryland had tried to obstruct the operation of a branch of the Second Bank of the United States by imposing a tax on all notes of banks not chartered in Maryland. 

However in the end, the court decided that Congress did have the power to create the Bank and the state of Maryland cannot impose taxes or else they will violate the Constitution.

cuban communists pressured the soviet union to place missiles in cuba.

"a government in which power is divided between state and national levels". federalism is a system of government in which entities such and state and province, share power with the national government.