If the Senate votes down the same sex marriage plebiscite bill it will amount to one of the most undemocratic acts by the Senate in Australian history. The accepted conceptual and historical role of the Senate is and has always been either that of a ‘States’ house’ (where senators represent the interests of their State) or as house of review (where the Senate performs a more free-ranging and constructive role of vetting bills passed by the House of Representatives), or a combination of both.