Donald Trump has secured the necessary delegates to win the Republican presidential nomination for a third consecutive election. That result was never in much doubt, but the contest to be Trump’s running mate is harder to predict. Once again, the Republican primaries demonstrated his strength among white men in rural areas, leading to speculation that he will choose a woman or person of colour to broaden his appeal in November. Here are some factors to consider and a look at the likely contenders. Why does Trump need a new running mate? Former vice-president Mike Pence was a useful ally during...