Trump told Republicans to be on alert for what he claimed was a Democratic plan to rig the contest through increased use of mail-in voting- a measure Democrats say is needed to protect people from catching COVID-19 in crowded polling stations. Opponents say Trump's increasingly extreme resistance to expanded mail-in voting is an attempt to suppress voter turnout, while setting up an excuse to challenge the result if he is defeated.

from Times of India https://timesofindia.indiatimes.com/world/us/us-presidential-elections/trump-gets-republican-nomination-and-claims-election-being-rigged/articleshow/77732238.cms