Barack Obama has ad mitted it was "boneheaded" to get involved in a land deal with Tony Rezko, his friend and fund-raiser. But the media's focus on that deal has distracted from the bigger question: Why would Obama become involved in any deal with a man like Rezko, who made his living sponging off taxpayers and corrupting public officials? Because, by the time of the deal, the two already had a long relationship of mutual benefit. The deal's details are well-known: On June 15, 2005, Obama bought a gorgeous house in Hyde Park for $1.65 million - $300,000 below the...