ABC announced today that Good Morning America's anchor duo of Charlie Gibson and Diane Sawyer will fill in for Bob Woodruff on World News Tonight. As everyone knows, Woodruff suffered severe injuries in an IED explosion in Iraq. Because his injuries will keep him out of action indefinitely, ABC News president David Westin decided to preserve the dual-anchor format that Woodruff and Elizabeth Vargas started on January 3. To that end, Gibson and Sawyer will take turns co-anchoring WNT with Vargas until Woodrufff is well enough to return.

I would imagine that both Gibson and Sawyer won't venture out into the field much, so look for Vargas to be taking the "intrepid reporter" role so that Westin's vision of having at least one anchor in the field can continue.

The irony, of course, is that Gibson was passed over for Vargas and Woodruff when the permanent pairing was announced in December.