Trump himself said Flynn had to resign for lying to the vice president about Flynn's contact calls with the Russian ambassador. FBI rightly believed Flynn's lie made the national security adviser susceptible to Russian Kompromat. So any Flynn lie to FBI about the Russian ambassador to include numerous matters Russian was material to the investigation. Live with it even though it leaves the Rowers with nothing.
Ok-- Flynn had to be fired. Thats fine. At best the man can't accurately impart information to his supervisors and that is not a good quality in a NSC director, I would think.
But there is no law against it.
The FBI can't just walk around and investigate people because they feel like. What do you think this is-- Russia?
Flynn compromised himself to your Russians. It hasn't ever been the job of the FBI to help Flynn to Houdini himself in a national security pinch that involved your Russia in any way. You're so wandering and desperate you're making statements a 5th grader would crumple up and toss.
Part of the problem here is that the FBI DIDNT think he was a security threat-- in the beginning of January they were moving to close the investigation they had on him.
As far as Flynn being compromised by Russia, a 5th grader should realize that as the USA knew what Flynn spoke about with the ambassador, it is laughable that somehow Flynn was compromised.