More than two years after her upstart Senate campaign rocked the Delaware political world, Christine O’Donnell got an unexpected contact from a U.S. Treasury Department agent warning that her private tax records may have been breached. The phone message earlier this year shocked the battled-scarred candidate, a tea party favorite who knocked off Republican mainstay Michael Castle in the primary before losing in a bid to win Vice President Joseph R. Biden’s former seat. “Ms. O’Donnell, this is Dennis Martel, special agent with the U.S. Department of Treasury in Baltimore, Md. … We received information that your personal federal tax...