Including his public statements on the matter advocating private gun ownership. Certainly not his background as a Constitutional Law Professor.
Obama is, was and remains one of the most authoritative serving politicians on the Constitution and he has not indicated anywhere in his career that he intends to remove legal firearm ownership.
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, although not full-time or tenure-track.[1]
[1]http://www.factcheck.org/2008/03/obama-a-constitutional-law-...
Note: My guess is that he, like most sane adults, question the need for possession of a or multiple military-grade rifles or sub-machines capable of killing considerable numbers of human beings in a short space of time.
It's not about taking away the 2nd Amendment. It's about Amending it to make it compatible with modern life whilst maintaining the spirit of the law.