Actually, if Sessions recused himself then he cannot involve himself in referring indications of criminality to a criminal prosecutor. That would amount to un-recusing himself.
This is all Rosenstein’s matter to handle entirely.
I think the recusal is why Sessions treaded so lightly with Huber. He merely asked Huber to evaluate certain concerns raised by Grassley’s committee. He didn’t authorize a criminal investigation.
If Sessions were to appoint a special counsel to commence, or direct another US Attorney like Huber to commence, a criminal investigation into the Mueller team which is criminally investigating Trump (and Sessions) he opens himself to attack that he is violating his recusal or trying to obstruct an investigation into Trump and himself.
Now perhaps Huber might elect to open a criminal investigation on his own. With no direction from Sessions. But Rosenstein could shut that down pretty quickly if he wanted to.
“if Sessions recused himself then he cannot involve himself in referring indications of criminality to a criminal prosecutor.”
He did.
He must have determined that it was not covered by his recusal.
“He didn’t authorize a criminal investigation.”
Not in the letter to Congress that was made public. We don’t know what was said or written to Huber.
As you noted, Huber has the authority to prosecute crimes on his own (and could be liable for failing to do so), no matter how he finds out about them.