US Republican presidential candidates have taken aim at Donald Trump for failing to show up at their latest televised debate. The event, hosted by Fox Business in California, saw Mr Trump's rivals stepping up their attacks on him in an effort to put a stop to the former president's commanding lead in the polls ahead of the election next year. Instead, Mr Trump went to the key state of Michigan to deliver a speech amid the backdrop of a car manufacturer's strike. Candidates in California were asked about education, economic policy and the border with Mexico in a wide-ranging debate...