WASHINGTON — The FBI has refused to give Congress an informant file alleging that President Biden took bribes while he was vice president, The Post has learned — setting up a possible showdown over access to the information. House Oversight Committee Chairman James Comer (R-Ky.) issued a legally binding subpoena last week requiring the FBI to turn over the file by noon Wednesday, but the FBI responded instead with a six-page letter raising various objections. “Information from confidential human sources is unverified and, by definition, incomplete,” wrote FBI acting assistant director for congressional affairs Christopher Dunham, who also argued that...