Is logical equivalence itself a proposition? I understand that the biconditional $P \leftrightarrow Q$ is a hypothesis that may be true or false depending on the truth values of P and Q.
Furthermore, I understand that the logical equivalence $P \Leftrightarrow Q$ is the assertion that the biconditional is a tautology, i.e. that the hypothesis is true.
However, isn't $P \Leftrightarrow Q$ itself a proposition? After all, it is equivalent to the statement that $P \leftrightarrow Q$ is tautologically equivalent to $T:$ $$(P \Leftrightarrow Q) \Leftrightarrow ((P \leftrightarrow Q) \Leftrightarrow T).$$ Is this a circular? Or is there some "higher form" of equality that logical equivalence lives in?

It is an equivalence in a metalanguage, which loosely speaking is a "higher form" of equality. Basically saying that $P\Leftrightarrow Q$ says that "$P$ is true if and only if $Q$ is true", where being true is something derivable from the rules of propositional logic. This is different from saying "$P\leftrightarrow Q$ is true", since the latter is a statement in propositional logic, whereas the former is a statement about propositional logic.
Read about metalanguages on the wikipedia article.
