I think that under Federal sentencing rules a judge has limited (at best) flexibility when passing sentence.IOW,if a conviction in Federal court carries a max of 20 years I doubt that the judge can say "no time".A lawyer,of course,could set me straight if I'm wrong.
I would have to look at the guidelines to be sure, but I believe he's in the first zone (A), which means the judge would have the flexibility to sentence him to federal probation, only.
My only caveat is I think there's an enhancement for obstruction, which might bump him to the next level inside that zone, which could mean mandatory prison time.