TO THE BEST OF MY ABILITY From Allen Weinsten's essay on how Theodore Roosevelt tested the limits of the presidency to a new essay by James Chase on the George W. Bush administration, this book delivers thoughtful analyses of the men who have led this country.   "What a wonderful way to learn about our American presidents. This handsomely illustrated volume - with essays by our nations finest historians - brims with fresh anecdotes, stylish prose, and sharp analysis. A treasure!"  -Stephen E. Ambrose, author of Band of Brothers