[Frumious Bandersnatch]

You will note that the state governments can't exercise these powers.  If they try to, it goes against the supremacy clause.  By seceding, the states are asserting that the supremacy clause is null and void, since they are making a law which is superior to the constitution.  Not to mention the fact that they are also asserting a sovereignty not granted them under the constitution.

[4CJ]

By seceding, the states are asserting that the supremacy clause is null and void, since they are making a law which is superior to the constitution.

You still don't understand. Nothing prohibits secession, or even sovereign state laws. Unless the Constitution somewhere is delegated the power over secession (or anything else), the US Constitution cannot prohibit secession. Read Hamilton in Federalist 84 for a clue about excersing powers not delegated. He (and other federalists) argued against a Bill of Rights, simply because the federal government had not been delegated the powers over religion, speech, RKBA, individual liberties, civil cases, jury trials, search & seizure &c.

Not to mention the fact that they are also asserting a sovereignty not granted them under the constitution.

Read amendment X. What part of it do you not understand? The states retain EVERYTHING no delegated nor prohibited. The supremacy clause does not delegate or prohibit any powers - it just recognizes that where a power has been delegated, the Constitution is supreme.