McCulloch v. Maryland
How much power does Congress have?
Can Congress institute a national bank?
Ultimately, the questions at hand were if Congress was allowed to establish the bank, and if Maryland unconstitutionally interfered with congressional powers.
Congress has constitutional authority under the Elastic Clause
The Supreme Court under John Marshall unanimously decided that Congress held the constitutional right and authority to institute the Second Bank of the United States under the terms of the Elastic Clause. This allowed them to institute whatever was "necessary and proper" for the nation, which in this case was the bank. Therefore, Maryland could not tax the national bank, since it was established with supreme constitutional powers.