If Michal Flynn informed Donald Trump about his multiple conversations with the Russian Ambassador about rolling back President Obama's sanctions to punish Russia for interfering in the US election, it's an impeachable offense for now-President Trump.
It would mean that while still a civilian, Trump violated the Logan Act which makes it a crime for civilians to engage in diplomatic negotiations with foreign governments in a dispute with the United States.
Either Flynn was freelancing, which seems unlikely for a matter of such gravity. Or he was representing his boss, the Donald, which makes the Donald equally guilty.
The Senate must hold hearings on Russia's dangerous interference in American elections and diplomacy.
And they must call Michael Flynn to testify under oath about what Trump knew about Flynn's discussions with the Russian Ambassador and when Trump knew it.
If , as is likely if Flynn doesn't perjure himself, Trump knew what was going on, then Trump must be impeached for violating the law and putting American security in danger.