MSNBC: Sen. Barbara Boxer held a hearing Wednesday to find out why the Bush administration has put off deciding whether to list the polar bear as a threatened species. But her star witness, Interior Secretary Dick Kempthorne, didn’t show. "This listing is months overdue, in violation of the Endangered Species Act," the California Democrat said at the hearing of the Senate Environmental and Public Works Committee. Witnesses who did make it to the hearing said that given …