The FBI has confirmed to a senior Republican senator that agents were sworn to secrecy -- and subject to lie detector tests -- in the Hillary Clinton email probe, an extensive measure one former agent said could have a "chilling effect." A July 1 letter sent by a senior deputy to FBI Director James Comey to Senate Judiciary Committee Chairman Charles Grassley, R-Iowa, detailed the restrictions on agents. The letter, reviewed by Fox News, confirmed agents signed a "Case Briefing Acknowledgement" which says the disclosure of information is "strictly prohibited" without prior approval, and those who sign are subject to...