There are things President Barack Obama can't say and do while he's still in the White House, but he said this week once he leaves office, he may become more active in the issues in which he believes.

"Having had this office has given me this incredible perch from which to see how the world works," Obama said in a Vanity Fair interview with presidential historian Doris Kearns Goodwin. "The power of the office is unique and it is a humbling privilege," Obama said. "With that power, however, also comes a whole host of institutional constraints. There are things I cannot say. There are things that..."

"You mean now, but you will later," Goodwin interjected.

"That I cannot say, not out of any political concerns, but out of prudential concerns of the office," Obama added. "There are institutional obligations I have to carry out that are important for a president of the United States to carry out, but may not always align with what I think would move the ball down the field on the issues that I care most deeply about."

Obama, who will leave office at 55, will be younger than many former presidents, and there are causes he feels passionately about, including violence against black men.

For instance, the president said after the shooting death of Trayvon Martin in Florida that the teen could have been "my son" or that he "could have been me, 35 years ago."

Obama also commented that as the inauguration approaches and he leaves office, he'll have moments where he feels "melancholy or nostalgic," especially about leaving his team, but he knows when it's time to let the office go.

"The team that you build here, the family that you build here, is powerful," said Obama. "But there is a reason why George Washington is always one of the top three presidents, and it's not because of his prowess as a military leader; it's not because of the incredible innovations in policy that he introduced. It's because he knew when it was time to go.

"And he understood that part of the experiment we were setting up was this idea that you serve the nation and then it's over, and then you're a citizen again. And that 'office of citizen' remains important, but your ability to let go is part of the duty that you have."