President Trump’s first national security adviser, Michael Flynn, pleaded guilty Friday to lying to the FBI about his contacts with the Russian ambassador during the transition, and he is cooperating with the special counsel’s investigation into Moscow’s interference in last year’s election.

Flynn told investigators that he was instructed to engage with the Russians by senior members of the Trump transition team.

The plea agreement marks a major development in special counsel Robert Mueller’s probe — Flynn is the first former senior official from the Trump White House to face charges. It also suggests that Flynn has information that may take investigators to the core question of their inquiry: possible coordination between the Trump campaign and Russia.

Because Flynn agreed to a plea deal on just one charge, we can be sure he is ‘singing like a canary’ to Robert Mueller, and that means Donald Trump is likely in the crosshairs of an investigation that could make Trump the first US president thrown behind bars.