There is History of Punishment Reform

America: A History of Mandatory Minimums
Mandatory minimum sentences for federal drug offenses began in 1950 with the Boggs Act. Enhancements were increased on federal penalties for drug law offenses in 1956.  These laws remained on the books for 14 more years until the congress cleared the books on these laws. 

Erasing Mandatory Minimum Sentences: It can be done
In 1970, Congress passed the Comprehensive Drug Abuse and Control Act, which repealed the Boggs Act. The Democratic Congress cited that mandatory minimum sentencing were ineffective in combating.  The Federal Government restored mandatory minimum sentencing in the mid-1980's, but it is possible for sentencing reform.