And not just the Trinity, but any and every fundamental tenet of Christianity. If a Christian does not find the Trinity in Scripture, no force or argument on earth can declare him wrong.
No appeal to education will work, because Scripture trumps education, and besides, the meaning of Scripture is clear, is it not?
No appeal to creeds or confessions will work, because Scripture trumps creeds and confessions.
No appeal to Councils will work, because Scripture trumps Councils. If Councils did have such authority all Protestants would be Catholic.
No appeal to Tradition will work, because Scripture trumps Tradition. If Tradition did have such authority all Protestants would be Catholic.
There is, quite simply, no possible way to state with authority that a Christian who does not find the Trinity in Scripture is wrong. There are no right or wrong interpretations of Scripture, only those which are more popular and those which are less popular. And the more popular ones can rightly be described as nothing more than Catholic baggage that has not (yet) been discarded.