If that were true, then the United States Supreme Court would be an idle mechanism. They may not interfere "while" Congress is performing it's function, but they can rule if the process is constitutional, should such a case be brought before them.
In other words, Congress can do whatever the hell it likes, but if, in so doing they create a law that by proposition or process is unconstitutional, and the case is brought before them, then the Court can do whatever the hell it likes...