Columnist Jason L. Riley writes:  Why did the University of Pennsylvania hold Liz Magill to a higher standard than Harvard is holding Claudine Gay? Both presidents were guilty of indulging antisemitism on campus, repeatedly equivocating on what should have been a straightforward response to the Oct. 7 terrorist attacks on Israel, and embarrassing their institutions when testifying before Congress. Yet Ms. Gay has kept her job and Ms. Magill has been shown the door. You don’t need a Harvard degree to understand that Ms. Gay, the school’s first black president, advances the diversity imperatives of her institution in ways that Ms. Magill, who is white, doesn’t.