When the Tea Party erupted in the spring of 2009, both US political parties were quick to define it. Democrats depicted the anti-tax agitation as “AstroTurf” – faux populism staged by conservative millionaires. Republicans saw it as an authentic backlash against Washington’s bail-outs. Both were partly right. Neither could have forecast the damage the “take America back” crowd would inflict on Barack Obama – in last year’s midterm elections and since.

The differences between Tea Partiers and the Occupy Wall Street protesters are greater than their similarities. Yet the latter offer just as instructive a Rorschach test of American opinion: people read into both what they will. Some time in the near future, the staying power of OWS protesters is likely to be tested: New York has already suffered a wintry cold snap over the weekend.

Whether OWS proves more durable than many expect – and turns from a protest into a movement, like the Tea Party – the war of definition has consequences. From Bill O’Reilly, the Fox News anchor, to Herman Cain, the former pizza executive and now improbable Republican frontrunner, most conservatives dismiss the protesters as a “bunch of far-out hippies” and “ragtag anarchists” – to cite a couple of recurring monikers.