Polling explainer: is the race for the White House tightening?

Betting markets have moved dramatically in Donald Trump’s favour despite Joe Biden’s stable lead
Some state polls suggest Donald Trump is gaining on Joe Biden, but there are reasons to be sceptical © Bloomberg/AP

Following the party conventions and the unrest in Kenosha, Wisconsin, there is evidence that the US presidential race between Joe Biden and Donald Trump has started to tighten in the all-important swing states.