Fewer and fewer people ask Jeremy Wariner how a white guy can be so fast, and under most circumstances that would be a relief. Only now people are wondering something almost as indelicate about Wariner, the slender Texan who in 2004 became the first white American to win an Olympic sprint medal in 40 years. Essentially, people want to know if he’s nuts. “What in the world is he thinking?” Deon Minor, Wariner’s business manager, said recently with a grin. “Why did he leave Clyde? “ … That’s what people want to say, but they won’t say it around us.”