This will upset The West Wing tragics among us, but it's wrong to call Labour's method of electing its leader a primary. It creates the impression of far greater democratic participation than the reality.
A more accurate analogy in US politics is a caucus, a means of intra-party voting that attracts a smaller, less representative, coterie of hardcore activists.
Take two early contests during the 2008 Democratic nomination battle between Barack Obama and Hillary Clinton: in South Carolina, a state with a similar population to New Zealand's, more than half a million people voted in the primary; in Iowa, with a population of just over three million, 15,000 diehards participated in the caucus.
According to figures leaked to the media, only around 5000 members took part in the election of David Cunliffe in 2013. It may seem an improvement on MP-only ballots, but the process falls way short of earning the title "primary".
The caucuses that more closely resemble Labour's approach are widely considered outmoded, undemocratic and politically fraught in the US. Politicians in Nevada last year moved to abolish their state's caucus because it "disenfranchises voters", advocating a primary instead.