In a wide-ranging exclusive interview with TODAY's Savannah Guthrie, Defense Secretary Ashton Carter says he's "confident" the United States and its coalition of allies can defeat ISIS, but says the victory could take time.

"It's going to depend on how quickly we're able to build the forces that will sustain the defeat. It's the lasting nature of the defeat that's really key," Carter explained.

Carter also addressed:

The nuclear talks with Iran: "The military option will remain on the table. If there is a good agreement to have, obviously it's worth waiting for and completing the negotiations."

"The military option will remain on the table. If there is a good agreement to have, obviously it's worth waiting for and completing the negotiations." Asked whether he laughed or cringed when he saw the video of Vice President Biden getting up close and personal with his wife at his swearing-in, Carter replied: "I laughed. They know each other extremely well. We're great friends of the Bidens."

"I laughed. They know each other extremely well. We're great friends of the Bidens." On whether the White House made a mistake in saying Bowe Bergdahl served with distinction when there were questions of him walking off the base: "I really don't want to get into that. We do have a principle that we bend over backward in favor of trying to return an American service member."

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