[The Green Goblin]

And it be further enacted, That whenever the laws of the United States shall be opposed or the execution thereof obstructed, in any state, by combinations too powerful to be suppressed by the ordinary course of judicial proceedings, or by the powers vested in the marshals by this act, it shall be lawful for the President of the United States to call forth the militia of such state to suppress such combinations, and to cause the laws to be duly executed.

There is nothing in the Constitution which forbids the secession of states, so this argument of yours is irrelevant.

[Metal4Ever]

There is nothing in the Constitution which forbids the secession of states, so this argument of yours is irrelevant.

If you want to make that argument, the flipside to that coin is that there's nothing in the Constitution that says that the Federal Government can't wage a war to return the seceeding states back to the Union.