Not only does the actual text of the Constitution prohibit unilateral state secession, but the laws made in pursuance also do so. Specifically, the Militia Act of 1972 gives the president the clear power to enter any state and ensure that United States courts are operating.
Oddly enough, Jefferson Davis would have heartily agreed with your article.
He held that language in the constitution of the so-called CSA that was identical to the Costitution's language gave Congess the power to act in the common defense of the government, thus giving the lie to the complete state sovereignty that the so-called seceded states claimed to have. How about that?
See "Battle Cry of Freedom", by James McPherson, p. 433.
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