In a note out this past week, Citi's FX team called a disputed election the 'biggest political risk' in the world.
They wrote:
We view most of the recent price action in G10 FX (with the possible exception of the USDJPY rally) as being the result of squaring up ahead of the US election and 18th National Congress of the Communist Party of China. The biggest political risk is the potential that the US result won‘t be known due to the combination of a tight election and re-count/mail-in issues in swing states.
They cited the possibility of a nail-biter in Ohio that doesn't get resolved for days, as mail-in ballots take a long time to get counted.