Vice President Joe Biden and Dr. Jill Biden thank nurses during a Christmas Day visit to Walter Reed National Military Medical Center, in Bethesda, Maryland, Dec. 25, 2013.

Vice President Joe Biden and Dr. Jill Biden thank nurses during a Christmas Day visit to Walter Reed National Military Medical Center, in Bethesda, Maryland, Dec. 25, 2013.

Vice President Joe Biden and Dr. Jill Biden thank nurses during a Christmas Day visit to Walter Reed National Military Medical Center, in Bethesda, Maryland, Dec. 25, 2013.