Note the second clause of section 1 of the Thirteenth Amendment:
Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction.
It's entirely legal to use convicted criminals as slaves in the penal system. A term "at hard labor" was well established at the time of this emancipation amendment, which was clearly crafted to avoid interfering with both the penal system and requirements to provide restitution.
The amendment was directed at ending inherited states of slavery and heading off enslavement of innocents and re-legalization of importation of slaves.
By the wording it's even constitutional to write laws that sentence them slavery and sell them (though not make their slavery inheritable or contagious to their relatives, both because they're not themselves convicted and because of the prohibition on "corruption of blood" in article III section 3.). Given the history of slavery and emancipation I suspect no such law will ever be passed and the courts would consider this history and interpret the wording to strike down such a law if it were passed.
= = = =
"Obama’s Economists: ‘Stimulus’ Has Cost $278,000 per Job."
That means: For each job "created or saved" about five were destroyed.