If you lie to a US Federal agent, they can bust you, and my understanding is that judges like to sentence those convicted of this by juries to jail for long periods of time. But, if you are charged with this crime and plea guilty, so there is no jury trial, then there is room to negotiate.
Note that FBI agents know how to make sure prosecution will get a conviction. They write everything down carefully, have witnesses, etc. So, if they ask you a question and you lie, you are now in the process. It is just a matter of time until you are signing a plea agreement.
Michael Flynn, perhaps owing to hubris, perhaps owing to fear, perhaps owing to sub-average intelligence, perhaps to a combination, managed to lie, apparently multiple times, to FBI agents.
Unlike most of the other characters in the Trump-Russia scandal, Flynn has been more involved in Turkish shenanigans than Russian, but the charges going down today do relate to Russia.
He is charged with lying about his interactions with the Russian ambassador to the US about sanctions, and about a pending UN Security Council resolution related to Russia.
Here is the charging document: Continue reading Flynn Lied to the FBI; Here is the charging document