President Barack Obama has opted to make some changes to the federal criminal justice system on his own, rather than waiting for Congress to pass an overhaul measure during an election year. And his new solitary confinement rules have already won the praise of one GOP presidential candidate.

Solitary confinement will no longer be used on juveniles or individuals accused or convicted of low-level crimes, Obama announced Monday in a newspaper op-ed. He also is expanding treatment for the mentally ill and ramping up the amount of time inmates subjected to solitary confinement get to spend outside their cells. Collectively, the changes will affect 10,000 federal prisoners, according to the White House.

Those changes stemmed from an Obama-ordered Justice Department review of federal solitary confinement policies that began last summer. That review determined holding prisoners in solitary can be a “necessary tool” in instances such as prisoners needing to be in isolation for their protection, Obama wrote in the opinion piece in the Washington Post.

“In those cases, the practice should be limited, applied with constraints and used only as a measure of last resort,” the president wrote.

The White House claims up to 100,000 people are being held in solitary confinement in American prisons, with as many as 25,000 serving “months, even years of their sentences alone in a tiny cell, with almost no human contact.”

But Solitary Watch, a wing of the non-profit Community Futures Collective, says “the number of people held in solitary confinement in the United States has been notoriously difficult to determine.”

“The lack of reliable information is due to state-by-state variances and shortcomings in data gathering and ideas of what constitutes solitary confinement,” according to a Solitary Watch fact sheet. “With that said, currently available estimates suggest between 80,000 to 100,000 incarcerated persons are held in some form of isolated confinement.”

A bipartisan pair of senators, including a Republican presidential candidate, were quick to praise Obama’s move.

“Sen. Booker and I have strongly advocated for this to happen, I am supportive of the idea of ending juvenile solitary confinement,” Sen. Rand Paul, a GOP presidential candidate, said in a statement to Roll Call.

The Kentucky Republican was referring to Sen. Cory Booker, D-N.J., with whom he has worked on criminal justice issues, including juvenile detention.

After the president’s opinion piece appeared, Booker highlighted his legislation to bar juvenile detention for juveniles in federal custody except temporarily when officials are dealing with behavioral issues or short-term threats.

“The president’s announcement is a step forward in restoring dignity to our criminal justice system and improving the way it treats children and nonviolent offenders,” Booker said in a statement. “Congress must now act to make the ban on juvenile solitary confinement a permanent part of federal law.”

The work of Paul and Booker underscore a broader level of support among Republicans and Democrats on Capitol Hill for a sweeping criminal justice overhaul measure. Obama also supports such a wide-ranging bill as he looks to lock in a handful of outstanding legacy issues during his final year in office.

Notably, Senate Judiciary Committee Chairman Charles E. Grassley, R-Iowa, also has signaled support for Obama’s solitary policy changes.

The Judiciary Committee passed a criminal justice overhaul bill last November by a vote of 15-5, with Republicans and Democrats supporting the measure. The bill has yet to reach the Senate floor. The House could opt to pass several smaller measures that would have to be reconciled with a broader Senate bill, making the path to Obama’s desk somewhat murky.

In the op-ed, Obama told the story of Kalief Browder, a 16-year-old who was sent to Rikers Island jail in New York after being accused of stealing a backpack. While detained there awaiting trial, Obama writes that the Bronx native “endured unspeakable violence at the hands of inmates and guards — and spent nearly two years in solitary confinement.”

He was released in 2013 after never receiving a trial. Browder, 22, committed suicide early last June.

“He completed a successful semester at Bronx Community College,” Obama wrote. “But life was a constant struggle to recover from the trauma of being locked up alone for 23 hours a day.”

The Justice Department review also produced a set of 50 “guidelines” across a range of prison issues that will be sent to all federal criminal detention facilities.

Contact Bennett at johnbennett@cqrollcall.com and follow him on Twitter at @BennettJohnT . Contact Lesniewski at niels@cqrollcall.com and follow him on Twitter @nielslesniewski .