Wrong again.
“In Luther v. Borden, 326 the Supreme Court established the doctrine that questions arising under this section are political, not judicial, in character and that ‘’it rests with Congress to decide what government is the established one in a State . . . as well as its republican character.’’
https://constitution.findlaw.com/article4/annotation18.html
That doesn’t contradict what I’ve said. The clause concerns the responsibilities of the Federal government. The only one, therefore, that can violate it, is the Federal government, if they were to fail to uphold those responsibilities.