Republicans in Wild West presidential showdown in Nevada

US Republican presidential candidates faced off in Nevada with Donald Trump poised for a third straight victory ahead of next week's all-important "Super Tuesday" votes. As the caucuses got underway, the billionaire real estate mogul was all but certain to triumph, with the big question being which candidate would come in second. The contest is the fourth for the Republican presidential candidates, with Trump so far winning in New Hampshire and South Carolina.