Final answer:
The Three-Fifths Compromise was the clause in the Constitution that enshrined slavery, allowing each enslaved person to count as three-fifths of a free person for representation purposes.
Step-by-step explanation:
The clause in the Constitution that enshrined slavery in the founding documents of the United States is B.) the Three-Fifths Compromise. This clause, embedded in the original Constitution, was a result of debates over the representation of enslaved individuals in the House of Representatives. The founders avoided using the term "slave", which shows the complexity of their views on slavery after the American Revolution. Nevertheless, the Three-Fifths Compromise clearly referred to enslaved individuals, counting each as three-fifths of a free person for representation purposes, despite them not having civil rights or ability to vote.
This clause was ultimately superseded by the Fourteenth Amendment, which granted citizenship and equal protection under the law, making provisions like the Three-Fifths Compromise obsolete and setting the stage for further civil rights progress.