It’s not a “Donald Trump” question, as Carney insinuates. The number of transfer students that Columbia College accepts each year is small. The reason is Columbia’s Core Curriculum, required classes that usually take up much of freshman and sophomore years. If you’re a transfer student, you have to figure out how to fit these classes into your schedule while at the same time taking classes that count toward your major.
That Obama transferred to Columbia and then was able to graduate two years later makes his situation unusual. How he accomplished this and what classes from Occidental were accepted as credit toward his degree from Columbia are questions of a sort that it is quite acceptable to ask of a candidate in a presidential campaign.