Even a favourite candidate for the US presidential nomination can stumble. Were Hillary Clinton to lose momentum in her bid to be the Democrats’ candidate, there is a rival in the wings Hillary Clinton announced her run for the American presidency in January 2007, and at the time her closest rival, a first-term senator named Barack Obama, trailed her by close to 20 per cent in the opinion polls. Last weekend, as she embarked upon her second bid for the White House, the former Secretary of State led other potential Democrat contenders by more than double that.And yet as Clinton restarted the engines on the formidable political machine which she and her husband have built over the past four decades, Martin O’Malley, a two-time former governor of Maryland, was meeting voters in