MIAMI — In the weeks leading up to the 2020 election, the head of a progressive advocacy group had $115,000 on hand and wanted to use it to support Senate Democratic candidates as they tried to make gains in the Republican-dominated chamber. Josh Weierbach, the executive director of the nonprofit Florida Watch Inc., took the advice of a longtime Democratic fundraiser and gave the money to a dark-money nonprofit, Grow United. He did it with the understanding that it would be used to help flip one state Senate seat in Central Florida and defend one in Miami-Dade, according to records that are pa...