A major criticism of the Constitution in recent years is that prior to the passage of the 13th Amendment it had maintained slavery as a national institution. Yet this claim does not match what took place at the Philadelphia Convention in 1787 nor is it reflected in what the document actually says about slavery itself.
In an opinion piece for the New York Times, establishment historian Sean Wilentz argues that contrary to recent statements by Democrat presidential candidate Bernie Sanders and others, the United States was not “founded on slavery,” calling this “one of the most destructive falsehoods in all of American history.”
Although many proslavery elements were present at the Constitutional Convention and strove to make slavery a permanent part of the Constitution, their efforts failed despite securing compromises that merely tolerated the existence of slavery rather than endorse it. Wilentz writes:
“James Madison (himself a slaveholder) opposed the ardent proslavery delegates and stated that it would be “wrong to admit in the Constitution the idea that there could be property in men.” The Constitutional Convention not only deliberately excluded the word “slavery,” but it also quashed the proslavery effort to make slavery a national institution, and so prevented enshrining the racism that justified slavery.”
Full commentary @ The Tenth Amendment Center http://tenthamendmentcenter.com/2015/09/23/constitutionally-slavery-was-not-a-national-institution/
California Libertarian Report 