1790.......James Madison, “the Father of the Constitution” expressed his view on the government and the status of the States as they ratified the new constitution when he said,
“In order to ascertain the real character of the government, it may be considered in relation to the foundation on which its…ordinary powers are to be drawn…founded on the assent …of the people …to be given by the people, not as individuals composing one entire nation, but as composing the distinct and independent States to which they respectively belong. It is to be the assent and ratification of the several States, derived from the supreme authority in each State, the authority of the people themselves…Each State, in ratifying the Constitution, is considered as a sovereign body, independent of all others, and only to be bound by its voluntary act”.
But the question on the table is whether our Founders' Original Intent was that states could "at pleasure" unilaterally declare secession.
I've seen nothing to support claims they did.