> The original purpose of the federal courts was to ensure a neutral forum for the enforcement of federal laws
The Constitution is a federal law; the enforcement of the Constitution -- including against State violations -- is included within the enforcement of federal law. This is fairly express in the Constitution, and it was clear in practice in the first couple decades the Constitution was in operation.
Now, the protections in the Bill of Rights didn't extend to the States under the original Constitution, so its true that enforcing the Bill of Rights against the States was not part of that -- but not because the original design didn't involve the federal judiciary enforcing the federal Constitution against the States, but because that part of the federal Constitution didn't apply to the States. (And, technically, it doesn't now, either, however the current understanding is that 14th Amendment due process applies protects fundamental rights -- many of which are coextensive with, or at least closely approximate, those protected against federal encroachment by the Bill of Rights -- against state encroachment.)
The Constitution is a federal law; the enforcement of the Constitution -- including against State violations -- is included within the enforcement of federal law. This is fairly express in the Constitution, and it was clear in practice in the first couple decades the Constitution was in operation.
Now, the protections in the Bill of Rights didn't extend to the States under the original Constitution, so its true that enforcing the Bill of Rights against the States was not part of that -- but not because the original design didn't involve the federal judiciary enforcing the federal Constitution against the States, but because that part of the federal Constitution didn't apply to the States. (And, technically, it doesn't now, either, however the current understanding is that 14th Amendment due process applies protects fundamental rights -- many of which are coextensive with, or at least closely approximate, those protected against federal encroachment by the Bill of Rights -- against state encroachment.)