U.S. Sen. Barack Obama expressed regret late Friday for his 2005 land purchase from now-indicted political fundraiser Antoin “Tony” Rezko in a deal that enlarged the senator’s yard. “I consider this a mistake on my part and I regret it,” Obama told the Chicago Sun-Times in an exclusive and revealing question-and-answer exchange about the transaction. In June 2005, Obama and Rezko purchased adjoining parcels in Kenwood. The state’s junior senator paid $1.65 million for a Georgian revival mansion, while Rezko paid $625,000 for the adjacent, undeveloped lot. Both closed on their properties on the same day. Last January, aiming to...