It is impossible to deny the obstruction of congress. Trump has completely stonewalled.
Congress has the power of subpoena. The executive doesn’t get to decide they don’t have to comply because they don’t like what they are investigating. All previous attempts by Presidents to deny subpoenaed have been shot down by the courts. This is no different. A judge has already slammed Trump’s fictional “absolute immunity”.
Congress is a coequal branch. The executive must comply with subpoenas. If this was all so perfect, it shouldn’t even be an issue. Failure to comply is contempt, pure and simple.