I recommend two outstanding books by Raoul Berger on this topic:
1) GOVERNMENT BY JUDICIARY: THE TRANSFORMATION OF THE FOURTEENTH AMENDMENT; and
2) THE FOURTEENTH AMENDMENT AND THE BILL OF RIGHTS.
Also helpful is the section on 19th-century attempts to amend the Constitution to add a “separation of church and state” principle enforceable against the states in Philip Hamburger’s SEPARATION OF CHURCH AND STATE. In short, the dog didn’t bark: that is, advocates of the principle *never* said “we don’t need an amendment because we have the Incorporation Doctrine.”