Police sealed off the office building that houses Sen. John Kerry's headquarters on Thursday after a package with white powder was opened by campaign staff. Kerry, D-Mass., and his vice presidential running mate, Sen. John Edwards, D-N.C., were hundreds of miles away, campaigning their way toward next week's Democratic National Convention. "An envelope was opened and white powder fell out," said campaign spokeswoman Debra DeShong. "On the recommendation of the Secret Service, we contacted the local police who are here investigating."