Michael Flynn, the former Trump administration national security adviser, has invoked his 5th Amendment right against self-incrimination and is refusing to hand over documents to the Senate Intelligence Committee.

The documents in question are related to Flynn's contact with Russian officials during the 2016 presidential campaign. The Senate subpoena is a part of the ongoing investigation into possible collusion between the Trump campaign and Russia. A constantly evolving the story, the latest plot points have to do with Trump's firing of FBI director James Comey, who was leading the investigation into Trump-Russia collusion in the FBI, the appointment of a special prosecutor, and Trump's declassifying of highly-sensitive intelligence to Russian foreign officials in the Oval Office.

Flynn resigned in February when it was revealed that he misled Vice President Mike Pence about his contact with the Russian ambassador.

Source: npr.com