President-elect Donald Trump, a harsh critic of U.S. intelligence agencies, is working with top advisers on a plan that would restructure and pare back the nation’s top spy agency, people familiar with the planning said, prompted by a belief that the Office of the Director of National Intelligence has become bloated and politicized. The planning comes as Mr. Trump has leveled a series of social media attacks in recent months and the past few days against U.S. intelligence agencies, dismissing and mocking their assessment that the Russian government hacked emails of Democratic groups and individuals and then leaked them last...