The United States sees evidence that hackers, possibly working for foreign governments, are snooping on the presidential candidates, the nation's intelligence chief said Wednesday. Government officials are working with the campaigns to tighten security as the race for the White House intensifies. The revelation comes after director of national intelligence James Clapper's office released a document earlier this month saying foreign intelligence services tracked the 2008 presidential election cycle "like no other." The document was part of a slide show used to warn incoming Obama administration officials that their new jobs could make them prey for foreign spies.