[4CJ]

Here is the decision from Texas v White The Chief Justice references the Preamble and, indirectly, Article IV.

Future Supreme Court Justice Nathan Clifford (from Maine) once wrote regarding a state that, 'one of the foregoing fundamental principles of the American system of government, which is, that government is instituted by the people, and for the benefit, protection, and security of the people, nation, or community. And that when any government shall be found inadequate or contrary to these purposes, a majority of the community hath an indubitable, inalienable, and indefeasible right to reform, alter, or abolish the same.'

Undoubtedly the courts of the United States have certain powers under the Constitution and laws of the United States which do not belong to the State courts. But the power of determining that a State government has been lawfully established, which the courts of the State disown and repudiate, is not one of them. Upon such a question the courts of the United States are bound to follow the decisions of the State tribunals.
Chief Justice Taney, Luther v. Borden, 48 How. 1, 40 (1849)

It seems that the Supreme Court had already held 5-1 that the federal government did not have the authority to determine the validity of a state government, that was soley for a state to decide.

[Non-Sequitur]

And what does that have to do with Texas v White and the legitmacy of the southern rebellion?

[Non-Sequitur]

It seems that the Supreme Court had already held 5-1 that the federal government did not have the authority to determine the validity of a state government, that was soley for a state to decide.

"The fourth section of the fourth article of the Constitution of the United States provides that the United States shall guarantee to every State in the Union a republican form of government...Under this article of the Constitution it rests with Congress to decide what government is the established one in a State. For as the United States guarantee to each State a republican government, Congress must necessarily decide what government is established in the State before it can determine whether it is republican or not...And its decision is binding on every other department of the government, and could not be questioned in a judicial tribunal." -- Luther v Borden (48 US (7 How))

Taney didn't say that the federal government didn't have the authority to decide the validity of the state's government just the courts.