Now they have one in President Trump, who has pardoned five people in his first 17 months in office and bypassed the Justice Department’s recommendation system to do so. This week, he pardoned Dinesh D’Souza, the conservative commentator who pleaded guilty in 2014 to violating campaign finance law. Mr. D’Souza responded on Twitter by claiming victory over what he viewed as a political prosecution and by mocking Preet Bharara, the former United States attorney in Manhattan whose office prosecuted the case.

But by choosing to pardon political supporters whose cases largely failed to meet the basic guidelines for pardons, Mr. Trump could turn a slow and imperfect system into an unequal and unjust one, both liberal and conservative advocates warn, in which those with fame, money or access to the president’s ear are first in line to receive clemency.

“A more regular and robust use of presidential clemency, and a willingness to go around the Justice Department process, would be applauded by many,” said Kevin Ring, a conservative public policy expert and the president of Families Against Mandatory Minimums. “The issue is whether the president will still apply standards and meritocracy. Will he weigh the injustices and mete out justice to reflect the needs of a situation? That doesn’t seem to be the case.”

Mr. Trump has pardoned some people, like Joe Arpaio, the former Arizona sheriff convicted of criminal contempt for his campaign against undocumented immigrations, who did not serve out their entire sentences. And he said he might commute the sentence of Rod R. Blagojevich, the former Illinois governor, who in 2011 was sentenced to 14 years in prison for trying to sell the Senate seat vacated by President Barack Obama.

Their cases stand in stark contrast to those of Mr. Charles, whose plight has gained national prominence, or John Knock, who in 2000 was given two life sentences plus 20 years without parole for conspiracy to launder money and distribute marijuana. While in prison, Mr. Knock has taken and taught home-building classes, served as a mentor in the Fathers Behind Bars Discussion Group and has a clean disciplinary record, according to a petition created by his sister. Mr. Obama denied his application for a commuted sentence.