President Obama called a member of the Cambridge police department Friday to explain his statements earlier this week criticizing the arrest of Harvard professor Henry Louis Gates.

Obama reached out to Cambridge Police Sargeant James Crowley to explain his remarks earlier this week accusing the officer of "acting stupidly" in the arrest of Gates, which sparked a debate about race and policing in the United States.

"Because of our history, because of the difficulties in the past. African-Americans are sensitive to these issues," the president explained during a surprise appearance in Friday afternoon's White House briefing.

Obama spoke on the officer's "fine track record" when it comes to racial sensitivity, and joked that he'd invited Crowley to the White House to have a beer.

Obama defended his decision to speak on the arrest of Gates, first in Wednesday evening's prime time press conference, as an opportunity for a learning opportunity on racial issues nationally.

"My hope is that as a consequence of this event, this ends up being what's called a teachable moment," Obama said.

"There are some who say as president I shouldn't have stepped into this at all because I'm president and it's a local issue," the president added. "The fact that it's become such a big issue is indicative of the fact that race is still a troubling aspect of our society."