The FBI is under mounting pressure from the Senate to explain the circumstances behind a terrorist attack in Garland, Texas in 2015, although it's still far from clear whether the FBI intends to explain why an FBI agent was at the scene and did nothing.

In open testimony before the committee on Wednesday, FBI Director James Comey told Sen. Ted Cruz, R-Texas, that he would be willing to explain media reports that suggest the FBI may have had advance knowledge of the attack. But he only said he would do that in a classified briefing, and no briefing has been set.

Cruz's request was just the latest attempt to get to the bottom of the attack. Senator Ron Johnson, R-Wis., has been trying to get information from the FBI and the Justice Department for over a year and a half, and has had little to show for his efforts.