So the Sacred Magisterium can establish Sacred Tradition, to which they then appeal for their claims to be the Sacred Magisterium tahtthe Sacred Tradition establishes the Sacred Magisterium.
How convenient.
Yes, for consistent with the position in Catholic theology that one cannot know writings are of God except by faith in her which tells you ("no matter what be done the believer cannot believe in the Bible nor find in it the object of his faith until he has previously made an act of faith in the intermediary authorities..." - Catholic Encyclopedia>Tradition and Living Magisterium. "People cannot discover the contents of revelation by their unaided powers of reason and observation. They have to be told by people who have received in from on high."- Cardinal Avery Dulles, SJ, “Magisterium: Teacher and Guardian of the Faith,” p. 72; http://triablogue.blogspot.com/2008/08/magisterial-cat-and-mouse-game.html) and thus "when we appeal to the Scriptures for proof of the Church's infallible authority we appeal to them merely as reliable historical sources, and abstract altogether from their inspiration" (Catholic Encyclopedia > Infallibility) whereby it is supposed that one finds warrant for submission to Rome, then the basis for assurance that something is of God is that the Catholic magisterium has told you this. Thus as regards the (assumption of the) Assumption in sacred tradition, as the founder of Catholic Answers states,
“Still, fundamentalists ask, where is the proof from Scripture? Strictly, there is none. It was the Catholic Church that was commissioned by Christ to teach all nations and to teach them infallibly. The mere fact that the Church teaches the doctrine of the Assumption as definitely true is a guarantee that it is true.” — Karl Keating, Catholicism and Fundamentalism (San Francisco: Ignatius, 1988), p. 275.
But thus it follows that the basis for assurance that sacred tradition establishes the infallible magisterium is the the novel and unScriptural premise of ensured perpetual magisterial infallibility as per Rome (and basically in primary cults). Rome infallibly defines what sacred tradition consists of and means, and what she say it means is that Rome infallibly defines what sacred tradition consists of and means. If she does say so herself.
For again, Rome has presumed to infallibly declare she is and will be perpetually infallible whenever she speaks in accordance with her infallibly defined (scope and subject-based) formula, which renders her declaration that she is infallible, to be infallible, as well as all else she accordingly declares.
Of course, God calls souls to believe in Him based upon evidential warrant and the grace He gives to believe, and then progressively confirms this decision to the faithful. But Rome can only imagine that she provides the evidential warrant to believe her elitist claims, including her the novel and unScriptural premise of ensured perpetual magisterial infallibility.