"No, I'm not talking about Congress. I'm talking about the prosecutor. What kind of a mad prosecutor would try to send this guy up for 20 years or risk sending him up for 20 years?"

That was Justice Scalia today in the "fish case", Yates v. U.S., going after the government lawyer for his argument on the statute.   SCOTUSBlog has a summary of the oral argument, which looks like it was a rough ride for the SG's office:

Within minutes, Scalia leaned forward and, accusingly, told Martinez that he was defending the law and its use for someone who got only thirty days.  “What kind of sensible prosecutor does that?  Who do you have who exercises prosecutorial discretion?  Is it the same guy who brought Bond, last Term?” — a reference to a decision in which the Court had ruled that the Justice Department had gone too far in using a law against the spread of chemical weapons to prosecute a woman for trying to poison her husband’s lover.
Scalia pressed on, noting the potential for a twenty-year prison sentence under this law, and asking “what kind of mad prosecutor” would use that law in a case like this one?  Martinez weakly responded that the prosecutors had not asked for a twenty-year sentence against the fisherman.
Justice Ruth Bader Ginsburg then interjected, asking whether the Justice Department provided any guidance, “any kind of manual” to limit prosecutors.  Martinez answered that the manual for U.S. attorneys told them that, in choosing what crimes to charge, to go for the “most severe available.”
In view of that, Scalia retorted, the Court was going to have to be “much more careful” about how it interpreted federal criminal laws.  When Martinez tried to portray the fisherman as someone who ordered the destruction of evidence, disobeyed a federal officer, and worked out a cover-up scheme, Chief Justice John G. Roberts, Jr., commented: “You make him sound like a mob boss.”
Just what sentence did prosecutors recommend here, Justice Kennedy asked.  Martinez said twenty-one to twenty-seven months, but then added that thirty days here was “reasonable” and twenty years “would have been too much.”
The hearing’s tone had changed totally, and Martinez was on the defensive throughout the remainder of his time.  He tried to recover by going over the specific words and headings in the law, trying to show what Congress had intended for the law.
As he was nearing the end of his half-hour, Martinez was suddenly confronted by Justice Samuel A. Alito, Jr.   The lawyer, the Justice said, had a lot of arguments on the fine points about the law, but “you are asking us for something that is pretty hard to swallow,” that this law could be used for “really trivial matters.”
When Martinez protested that the law would not be used for “trivial matters,” Alito conjured up just such small offenses as throwing a single trout, illicitly caught, back into a lake, and then Justice Breyer asked about kicking a small ember away to try to conceal a forbidden campfire in a public park.  “You could multiple the examples beyond belief,” Breyer said.
In between those exchanges, Justice Kennedy commented acidly that the Court perhaps should no longer refer to the concept of “prosecutorial discretion” if it was open to use as in this case.
Martinez’s woe had started with Justice Scalia, and it never ended until he sat down.