US election 2020: Do postal ballots lead to voting fraud?

President Trump has criticised plans to expand postal voting in the forthcoming presidential election, claiming it leads to widespread fraud - but what evidence is there?

The US is in uncharted territory during the coronavirus pandemic as a record number of Americans are expected to vote by post.

Election authorities and the postal service have been put under immense strain processing the millions of extra ballots.

This has led to claims the system is unsafe and susceptible to manipulation.