How would peaceful, orderly secession -- the reclaiming of independence by a state or, in the case of Texas -- be "treason" against "the united States in Congress assembled"? By strict constitutional definition, "treason" consists only of "levying war against them" or in "adhering to their enemies, giving them aid and comfort."

Note how this passage refers to "states" in the plural, not to a singular national government. Interestingly, there is no language in the U.S. Constitution that makes "rebellion" against the general (or federal) government a form of treason. And since the federal government was designed to be an agent of the states, a state that chooses to withdraw from that relationship is hardly a "rebel."

Furthermore, secession is not an act of war, since withdrawing from a social arrangement of any kind is exactly the opposite of aggression.