Does the intent of the Framers that can be discerned from other sources have any part in deciding what is Constitutional, or does only explicit text in the document matter?
Yes. Original intent is about all that matters. Many people today, however, don't seem to notice the way they used words. You can find similar words in the same sentence (like national & federal, citizen & person) but they don't mean the same thing.
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The problem is that the cracking of the Republic began earlier. IMHO, with the Missouri Compromise.