Democratic Sen. Kamala Harris of California has scheduled her first campaign trip to Iowa before Election Day, stoking speculation about a potential 2020 presidential campaign. The first-term senator plans stops on Oct. 22-23 in what will be her first visit to nation’s leadoff presidential caucus state since she was elected in 2016. She was last in Iowa when, as San Francisco’s district attorney, she campaigned for Barack Obama’s 2008 presidential bid. Harris is among a large group of Democrats, including several senators, who are contemplating a challenge to President Donald Trump. She has won increased attention in recent weeks for...