Final answer:
The authors of the Southern Manifesto claimed that Chief Justice Earl Warren's decision was a threat to the US constitutional order because it weakened the principles of segregation and states' rights.
Step-by-step explanation:
The authors of the Southern Manifesto claimed that Chief Justice Earl Warren's decision was a threat to the US constitutional order because they believed it weakened the principles of segregation and states' rights. They argued that the decision infringed upon the rights of states to determine their own policies regarding racial segregation and interfered with the traditional social order of the South. The authors feared that the decision would lead to a breakdown of the constitutional order and create a precedent for federal intervention in other areas.