President Barack Obama said in a speech today that he has asked Attorney General Loretta Lynch to “start a review of the overuse of solitary confinement across American prisons.” He went on to challenge the practice as counterproductive as well as inhumane.

In a speech on criminal justice delivered at the annual convention of the NAACP in Philadelphia this afternoon, Obama said of solitary confinement:

Social science shows that an environment like that is often more likely to make inmates more alienated, more hostile, potentially more violent. Do we really think it makes sense to lock so many people alone in tiny cells for 23 hours a day for months, sometime for years at a time? That is not going to make us safer. It’s not going to make us stronger. If those individuals are ultimately released, how are they ever going to adapt? It’s not smart.

Earlier in the speech, Obama spoke of the need for reform in “the cellblock” as well as “the community” and “the courts.”

“While the people in prison have made mistakes, and sometimes big mistakes, they are still Americans,” he said. “We should not tolerate conditions in prison that have no place in any civilized country.”

After mentioning overcrowding, gang activity, and rape as “unacceptable” in prison, Obama made his remarks about solitary confinement.

Today is the first time the issue has ever been directly addressed by the President. His statement goes beyond any other criticism of solitary that has emerged from his administration over the past six and a half years.

New Attorney General Loretta Lynch, during her confirmation hearings, was asked by Minority Whip Dick Durbin asked her about psychologically damaging treatment of incarcerated individuals in solitary. Lynch responded by stating her willingness to have further “discussions” about both the constitutionality and overall use of solitary.

As U.S. Attorney for Eastern District of New York, Lynch was part of the U.S. delegation to the Convention on the Elimination of Racial Discrimination and made note of the “reduction of the use of solitary confinement” when listing evidence of the Department of Justice efforts to eliminate racial discrimination and uphold human rights.

Lynch was apparently referencing a small reduction in the numbers of individuals held in certain forms of solitary confinement by the federal Bureau of Prisons, as noted in an audit earlier this year.

Former Attorney General Eric Holder twice criticized the solitary confinement of youth—once in a 2014 video message, and once in reference to a DOJ investigation of conditions for adolescents on New York’s Rikers Island.

Obama’s promise to take action to limit solitary confinement, as well as his attack on mass incarceration, represent a shift in policy. The President has been a strong supporter of opening a second federal supermax prison in Thomson, Illinois, which will significantly increase the BOP’s capacity to house individuals in solitary confinement.

During the Obama Administration, the federal prison population rose from 201,688 in 2008 to a peak of 219,298 in 2013, then dropped to 208,102 as of this month. The Bureau of Prisons budget rose from $6.1 billion in 2009 to $6.9 billion in 2015.

Obama plans to become the first sitting president to visit a federal prison when he travels to El Reno Federal Correctional Institution in Oklahoma on Thursday. It remains to be seen whether he will tour the prison’s solitary confinement unit, as the National Religious Campaign Against Torture has urged him to do.

Given the political will, the President has the power to set limits on the use of solitary confinement in federal prisons, where according to the BOP’s own audit, more than 10,000 people are in some form of extreme isolation.