Jon Huntsman has quit the 2012 Republican presidential race with a call for candidates to cease personal attacks, often conducted through shadowy campaign vehicles known as super-Pacs.
These political action committees, which are transforming the nature of the US presidential races, can raise unlimited campaign contributions, so long as they spend the money without co-ordinating with the candidates they are backing.
However, the huge sums spent by the super-Pacs and the close ties between their operatives and the candidates have fuelled public cynicism about politics.
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