it's all about him. >> reporter: appearing on nbc's "today" show, wolff defended his portrayal of a deeply dysfunctional west wing. >> my window into donald trump is pretty significant, but even more to the point, i spent this -- i spent -- and this was really sort of the point of the book, i spoke to people who spoke to the president on a daily sometimes minute by minute basis. >> reporter: secretary of state rex tillerson told cnn's elise labbot he did not agree with those who questioned the president's ability to serve. >> i've never questioned his mental fitness. i have no reason to question his mental fitness. >> reporter: for a second straight day, allies of the president also defended his capacity for the oval office, a central question of wolff's book. >> this is just an absurd allegation by someone who has talked to a lot of disgruntled people at the white house. >> reporter: meanwhile, the president once again mocked the russia investigation, saying on twitter, collusion with russia is proving to be a total hoax, yet it's new questions about