Former FBI director James Comey is expected to testify before the Senate Intelligence Committee on Thursday.
Among the questions swirling: Whether President Trump asked Comey to end the FBI investigation into former national security adviser Michael Flynn.
If true, many Democrats say that amounts to obstruction of justice.
But what qualifies as an obstruction of justice? And where is the line between the inappropriate, and the illegal?
Nancy Gertner, former Massachusetts federal judge, senior lecturer on law at Harvard Law School and WBUR legal analyst.
This article was originally published on June 06, 2017.
This segment aired on June 6, 2017.