Obviously, you've never met any con law professors. And he wasn't a professor, he was an adjunct; there's a world of difference, so much so that most law schools don't use adjuncts to teach core subjects like con law unless they're in a bind.
From the University of Chicago Law School:
"UC Law School statement: The Law School has received many media requests about Barack Obama, especially about his status as "Senior Lecturer." From 1992 until his election to the U.S. Senate in 2004, Barack Obama served as a professor in the Law School. He was a Lecturer from 1992 to 1996. He was a Senior Lecturer from 1996 to 2004, during which time he taught three courses per year. Senior Lecturers are considered to be members of the Law School faculty and are regarded as professors..."
How could you be more wrong...