Tea party Republicans are now outraged again over Obama's presidential overreach, despite his constitutional power make such changes.
Vox: Conservative commentators and House Judiciary Committee chair Bob Goodlatte attacked the Obama administration for using executive power to solicit applications for commutation from inmates. They argued that Congress has the power to set punishments for federal crimes, and the executive branch doesn't have the power to change those punishments for particular criminals. Goodlatte accused Obama of "blatant disregard for our nation's laws and our system of checks and balances embedded in the U.S. Constitution."Here's a great explanation from Rachel Maddow that details how Reagan gave us overcrowded prisons with tough on crime mandatory sentencing.
The problem is that the Constitution does give the president broad power to issue pardons and commutations — there's no constitutional requirement that the office of the pardon attorney even exist, or that the president use it. The Heritage Foundation refers to the pardon power as "one of the least limited powers granted to the President in the Constitution."