Dr. Eric Whitaker and Sen. Barack Obama go way back. Their friendship began when they were graduate students at Harvard University. Now, Whitaker is one of Obama's closest advisers. Whitaker, 43, of Chicago, often travels with the presidential hopeful on the campaign trail and has vacationed with him in Hawaii. There's talk Whitaker could be in line for a federal appointment if Obama becomes president. Five years ago, Obama, then an Illinois state senator, gave a "glowing'' reference for Whitaker to Tony Rezko, the now-convicted political fixer who helped Gov. Blagojevich find people to run state agencies. Blagojevich hired Whitaker...