When word got out that the University of North Carolina system’s Board of Governors was holding an emergency session on Friday to meet with one finalist for the system’s presidency — and that the finalist was Margaret Spellings, a former secretary of education under President George W. Bush — it quickly became the topic of the day in higher-education circles. The news was the latest chapter in a series of highly divisive and politically charged episodes that began in January, when Thomas W. Ross, the system’s president, was pushed out by a Republican-led board. The board’s chair, John C. Fennebresque, at the time denied speculation that Mr. Ross’s ouster had been politically motivated but otherwise declined to explain the move.