U.S. on ‘unsustainable' budget course: CBO

``"The federal budget is on a course that cannot be sustained indefinitely," CBO director Douglas Elmendorf told reporters. "Because federal debt is already unusually high relative to GDP, further increases in debt could be especially harmful," the CBO report said. It said lawmakers would have to make "significant changes" to tax and spending policies to put the U.S. budget on a sustainable path for the long term.''