Why does the southern manifesto claim that the supreme court decision is a threat to constitutional government?

The Southern Manifesto is a text written in February and March 1956 by members of the United States Congress to express their opposition to racial integration in public places, and so their defense of segregation.

The document largely dealt with the historic landmark ruling by the United States Supreme Court on the segregation of public schools (Brown v. Board of Education). The first version was written by Strom Thurmond, with the final final version of Richard B. Russell. It was signed by 19 senators and 77 members of the House of Representatives, including the entire congressional delegation from the states of Alabama, Arkansas, Georgia, Louisiana, Mississippi, South Carolina and Virginia. With two exceptions, namely Republican Joel Broyhill and Richard Harding Poff of Virginia, all signatories were Southern Democrats.  

The Southern Manifesto accused the Supreme Court of "clear abuse of judicial power", thus violating the check and balances principles that are the basis of the federal government. It also stated that "all legitimate means would be used to repeal this decision, which was a contradiction to the Constitution, and would use the influence to prevent its entry into force."

the supreme court plays a big role in government. the constitution gives them ability to check the president and the congresses actions and dictate if their actions are allowed by the constitution or not.

hope this .