MONTGOMERY, Ala. —President Trump in his first term proved a windfall for the Southern Poverty Law Center, the antiracism nonprofit famed for its courtroom wins against the Ku Klux Klan decades ago. In 2017, the same year Trump took office and a white-nationalist rally in Charlottesville, Va., turned violent, annual contributions and grants to SPLC surged from $50 million to more than $130 million and have remained above $100 million nearly every year since.