I suspect that idiom means just the opposite of what you think it means. By "thankfully" I infer that you are relieved that the vast majority of political activity, "below the surface" of what is seen on TV, is nowhere near as reprehensible. Whereas "tip of the iceberg" is generally used to imply that the visible problem is merely a fractional indication of the much greater and uglier problem that lies beneath, being of the same matter and type of that which has already been seen.