The 14th Amendment is the one about citizenship, you are probably thinking of the 10th, "The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people." The US government could prohibit or regulate online gambling under Section 8, Clause 3 of the Constitution, "The Congress shall have Power To .... regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes".
"The voice of reason"
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