03/18/2010 05:12 am ET | Updated May 25, 2011

Charlie Gibson: Can Diane Sawyer Keep Viewers After 'Buzz' And 'Attention' Fade?

Charlie Gibson is going out with a bang — and is already casting doubts as to whether Diane Sawyer will succeed as his replacement.

As Gibson kicks off his final week anchoring ABC's "World News," the network has announced that he will sit-down with President Obama at the White House on Wednesday.

Gibson and Obama will "discuss a wide range of issues, including Afghanistan, the economy, and the President's reflections on his first year in office," the network said.

But what happens after he leaves? Gibson told the Washington Post's Howard Kurtz that Sawyer will "bring a buzz and an attention to this program that I could not," but he questions whether that will be enough to sustain an audience.

"That will bring a lot of people in the tent," he added. "But do you keep them?"

Gibson has been rumored to be disappointed with the selection of his former "GMA" co-host as his replacement.

Gibson also told Kurtz that the timing was right for him to call it quits.

"I'm whipped on a Friday night," Gibson told Kurtz. "I'm not as sharp as I once was, and I don't want to stay too long. . . . It's good to leave when your elevator is up on a high floor and not on a low floor."

Gibson also hinted that he sees less of a place for his style of broadcasting in a changing media landscape.

"Objectivity -- or the extent to which we strive for objectivity -- is less of a marketable commodity," he said. "People seem to want to hear news presented according to their own beliefs, and I don't understand that. I'm so much of a traditional, over-the-air broadcaster. I'm aware that it's changing, and I'm not adapting fast enough with it. Having hit the perfect arc of this business, I think it's time to move on."