If Michael T. Flynn informed Donald Trump about his multiple conversations with the Russian ambassador about rolling back President Barack Obama’s sanctions to punish Russia for interfering in the U.S. presidential election, it’s an impeachable offense for President Trump.

It would mean that while still a civilian, Trump violated the Logan Act, which makes it a crime for Americans “without authority of the United States” to engage in diplomatic negotiations with foreign governments in a dispute with the U.S. government.

Either Flynn was freelancing, which seems unlikely for a matter of such gravity. Or he was representing his boss, The Donald, which makes Trump equally guilty.

Congress must hold hearings on Russia’s dangerous interference in American elections and diplomacy.

And lawmakers must call Flynn to testify under oath about what Trump knew about Flynn’s discussions with the Russian Ambassador and when Trump knew it.

And if Senate Republicans refuse to hold hearings, the Resistance must occupy the offices of every Republican House and Senate leader.

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.