Stanford University economists estimate that President Donald Trump’s campaign rallies have resulted in 30,000 additional confirmed cases of Covid-19, and likely led to more than 700 deaths overall, according to a paper posted online this weekend. The research, led by B Douglas Bernheim, chair of economics at Stanford University, analysed data following 18 Trump rallies held between 20 June 20 and 22 September, three of which were indoors.