The contest for Republican and Democratic contenders to become presidential candidates in the United States has entered its third round.<br />Polls have already opened in the Republican primary vote in South Carolina, where frontrunner Donald Trump will try to fend off Ted Cruz.<br />Hillary Clinton and Bernie Sanders could face a close race in the Democratic Party caucus in Nevada.<br />The votes could be key ahead of the "Super Tuesday" round on 1 March.<br />On that day, about a dozen states will choose their candidates for the 8 November presidential election, with about a quarter of all nominating delegates up for grabs.
