Possible Clues:

• GOP head in the 2000s
• Monogram of the author of 'A Charge to Keep: My Journey to the White House'
• President before BHO
• Early 2000s White House inits
• 2001-09 U.S. pres
• This-century presidential monogram
• BHO predecessor
• 21st-century pres
• 43rd POTUS
• Prez with the same initials as an N.Y.C. landmark