Tango's Musical Terms: The Essential Elements of Music

Music's Essential Elements:  Melody, Harmony and Rhythm.  

If tango dancers really wish to dance musically, they must at least sense which of the three elements of music is the fundamental block.  I realize that there are many more elements (see link at the bottom), but let's keep this discussion on what is the essential of the essential.  Among these three blocks, even the focus is often questionable. which is the one essential one?  Are they all essential?  No. However, if you watch the camera man's focus on music performance, the limelight is often on the melody.  Also, much discussion on the Internet on the essential blocks starts with the melody.  It's true in tango that I often dance the melodic line, but the best musicians who play/sing the melodic line are exceptionally connected to where the rhythm is!  Are you?