The White House had to know he was using a fake name. Even 30 years ago they would perform an advance ID check before you could get press credentials to a presidential event. I would imagine that security is quite a bit tighter in the post 9/11 world.
The White House has gotten caught participating in this, and they need to make a statement and lay it to rest.
Participating in what? A reporter writes under an assumed name. He isn't the first and he won't be the last to do so.