Actually the republic was lost when one “honest” Abe Lincoln was allowed to walk all over the Constitution during the first 6 months of his first administration in order to prosecute his war of subjugation.
That opened the door through which every progressive since has walked.
I would agree that Lincoln opened the door—but Jefferson unlocked it when he decided to drop the proposed constitutional amendment that would have given the federal government the power to purchase land and to pursue the Louisiana Purchase under the power to make treaties. Economically, a great deal for everyone immediately involved—buying Spanish Territory from France for a steal—but making it much harder for the strict constructionists to maintain their position. If the federal government can find a penumbra of powers under the treaty clasue, what is to stop them from finding things in say, the commerce clause? If he had waited for the amendment to clear, we may or may not have ended up with the land, but he would have put strict constructionists in a much stronger position.