Actually, by the time of the 1860 election (Republican takeover of Congress and WH) the Dims had made slavery a national issue. The Dims' Fugitive Slave Trade Act of 1850 penalized people in free states for not helping capture a runaway slave. And the Dim majority Supreme Court rules in Dredd Scott that blacks are never, ever, ever going to be free American citizens.
It's very much like abortion was a national issue for the past 50 years until Trump put constitutionalists on the Supreme Court and overturned Roe. For half a century the Dims had made abortion a national issue even though the Constitution's enumeration clause says that abortion is a state issue. Only because Trump's SCOTUS picks brought abortion back to a state issue where it belongs can we say that abortion is now something that presidential candidates shouldn't push states for or against. There was nothing like that a century and a half ago overturning Dredd Scott and the Fugitive Slave Trade Act to make slavery back to being a state issue.
How so ?
Can a State randomly execute someone without charging them or without a trial, since that is not an enumerated power ?