It appears the FBI acted improperly to squeeze Mike Flynn

Alan Dershowitz:

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The FBI knew the truth. They had recordings of the conversations. Then why did they ask him whether he had those conversations? Obviously, not to learn whether he had them but, rather, to give him the opportunity to lie under oath so that they could squeeze him to provide incriminating information against President Trump. If you do not believe me, read what Judge T.S. Ellis III, who presided over the Paul Manafort trial, said to the prosecutors: “You do not really care about Mr. Manafort’s bank fraud. What you really care about is what information Mr. Manafort could give you that would reflect on Mr. Trump or lead to his prosecution or impeachment.”

Ellis continued: “This vernacular to ‘sing’ is what prosecutors use. What you have got to be careful of is that they may not only sing, they may compose.” Experienced criminal lawyers have seen this phenomenon at work. Most judges, many of whom were former prosecutors, have also seen it. But few have the courage to expose it publicly as Ellis did. Judge Emmet Sullivan of the District of Columbia Court also has expressed concern regarding federal prosecutorial practices in the investigation.

Defenders of the tactics used by special counsel Robert Mueller argue that his potential witnesses are generally guilty of some crime, such as lying to FBI agents, and that may well be true. But they are targeted not because of what they may have done. They are targeted for what they may know about what the real target may have done. Then they, and their relatives who may also be complicit, are threatened with imprisonment and bankruptcy unless they plead guilty and cooperate with prosecutors.

So the real question, which transcends the Flynn, the Manafort, and even the Trump investigations, is whether these tactics should be deemed acceptable to use in our justice system. Is it the proper role of law enforcement to conduct criminal morality tests to determine whether citizens will tell the truth or lie when given the opportunity to do either by FBI agents? Is it proper to target individuals for such tests for the purpose of pressuring them into becoming witnesses against the real target?

These are important questions for all citizens who care about civil liberties and prosecutorial abuses. They should not be addressed in a partisan manner. Instead, they should be answered by reference to the “shoe on the other foot” test....
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I would apply a "who was the victim test" to whether what Flynn did was a crime.  Certainly, the FBI was not a victim since they already knew the truth.  I have been in several depositions and hearings where lawyers have documents that may contradict what a witness is saying and it is not uncommon for the lawyer to show the document to the party testifying to ask if it refreshes his recollection of what really happened.  If the FBI was treating Flynn fairly and merely seeking information, that is what they would likely have done, instead of attempting a perjury trap.

Alan Dershowitz is, unfortunately, a rarity in the current environment.  He is a long time liberal who has not abandoned his sense of fairness and his respect for civil liberties even though the chances are remote that he voted for Trump.