Federal Sentencing Growth -- But Why?

This fun but scary interactive graphic over at the Wall Street Journal tracks the phenomenal growth in the number of federal criminal sentences handed out for particular crimes between 1996 and 2010, courtesy of data from the U.S. Sentencing Commission.

The sentence types that saw the biggest increases:  immigration offenses, gun offenses, national defense offenses, and child pornography offenses.  Sentence types that saw the biggest drops in raw numbers:  auto theft, burglary/breaking and entering, and gambling/lottery offenses (yes, those can all actually be federal crimes).

There may be many reasons for seeing increases in certain types of federal crimes and sentences.  Perhaps people are committing more of those crimes now than before, for example.  Or, perhaps police and prosecutors are simply enforcing those laws more than they were before -- the number of crimes hasn't increased, but we're catching and convicting more offenders than we were before.  Or, perhaps a host of factors -- the economy, public fears about crime, unemployment, social changes, internal policy changes in police departments and prosecutors' offices -- are prompting more convictions and sentencings for some crimes than for others.  Or, perhaps the increases in certain kinds of federal sentences are due to states deciding that they don't want to (or can't) handle prosecution of all of those crimes (immigration, for example, is constitutionally and historically the federal government's turf).  

But here's an interesting idea.  Illegal immigration was illegal (and a problem) before 1996, so why did the number of sentences start growing shortly after that year?  Could it possibly be because that's the year we created mandatory minimum sentences for federal immigration offenses?  Is it just a coincidence that the fastest-growing crime categories listed carry more than just a few mandatory minimums?  (See our full chart of federal mandatory minimums here.)  Is it possible that the mere creation of a federal mandatory minimum leads to a higher number of federal sentences for that crime?  If so, why?

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