A Washington D.C. law professor has given credence to Donald Trump’s charge that U.S. District Court Judge Gonzalo Curiel has a conflict of interest in a court case involving the likely Republican presidential nominee, saying the judge’s affiliation with a group that advocated for illegal immigrants creates “an appearance of impropriety.” Mr. Curiel’s membership and active role in the San Diego La Raza Lawyers Association, whether or not it creates an actual bias, is enough to disqualify him from presiding over the case, said Victor Williams, a professor at Catholic University’s Columbus School of Law. “The standard isn’t that one...