What single action could Obama realistically do before the end of his term that would make the biggest positive difference to his historical legacy?

He could make large scale and imaginative use of his power, sponsoring the pardoning of many tens of thousands of nonviolent prisoners. If he established a major new parole program, it might acquire momentum that a successor would feel it necessary to endorse. As the incarceration rate falls, so will the cost of keeping all these men and women in jail. In the first instance, these savings should be channeled to helping prisoners to adjust and to find work.