Comey's highly anticipated appearance before the Senate Intelligence Committee on Thursday could be a turning point in a controversy that has rocked Trump's young administration.
In his first public remarks since Trump fired him last month, Comey is expected to tell the Senate Intelligence committee that Trump asked him during a meeting in the Oval Office to end the Federal Bureau of Investigation's probe into ties between former White House national security adviser Michael Flynn and Russia.
Comey may also detail other conversations with Trump.