Read former FBI Director James Comey's opening statement to Senate intelligence committee

FILE- In this May 3, 2017, file photo, FBI Director James Comey listens on Capitol Hill in Washington. Comey's memo relating President Donald Trumpís request to shut down an investigation of his ousted national security adviser is a powerful piece of evidence that could be used to build an obstruction of justice case against the president. But criminal charges of interfering with an investigation are difficult in ordinary circumstances, several former federal prosecutors cautioned Wednesday, May 17, 2017, a day after word of the existence of the memo broke. (AP Photo/Carolyn Kaster, File) (The Minnesota Star Tribune)