From a Families Against Mandatory Minimums blog post:

Weldon Angelos was just 24 years old when he was sentenced to 55 years in federal prison for three marijuana sales… Angelos was convicted of selling narcotics while in possession of a firearm. These offenses fall under mandatory minimum sentencing laws, and prosecutors treated each of the three marijuana deals as its own individual offense. This is what is called “stacking” the charges, and it means Angelos was facing three prison terms, stacked on top of each other. All in– 55 years in prison, with no possibility of parole.

“A mandatory minimum is a sentence that says a judge has to impose a particular minimum number of years,” [former Federal Judge Paul] Cassell said. “It ties the judge’s hands… mandatory minimums can be used to send a message, but at some point the message gets lost.”