The trail of evidence starts with Trump’s attempt to get James Comey, the FBI director responsible for overseeing the investigation into Trump’s relationship with Russia during the 2016 election, to drop an investigation into National Security Advisor Michael Flynn.

When Comey refused, Trump fired him.

Trump made two more attempts at stopping the investigation by trying (unsuccessfully) to fire Robert Mueller, Comey’s predecessor. Then, Trump ordered White House Counsel Don McGahn to

create a false record

indicating that no attempts took place – McGahn refused.