PHILADELPHIA — Calling it an issue America can't afford to ignore, President Barack Obama laid out an expansive vision Tuesday for fixing the criminal justice system by focusing on communities, courtrooms and cellblocks. He announced a federal review of the use of solitary confinement and urged Congress to pass a sentencing reform bill by year's end.

In a speech to the NAACP's annual convention, Obama also called for voting rights to be restored to felons who have served their sentences, and said employers should "ban the box" asking job candidates about their past convictions. He said long mandatory minimum sentences now in place should be reduced — or discarded entirely.

"In far too many cases, the punishment simply doesn't fit the crime," Obama told a crowd of 3,300 in Philadelphia. Low-level drug dealers, for example, owe a debt to society, but not a life sentence or 20-year prison term, he said.

With his speech to the prominent African-American advocacy group, Obama sought to put a spotlight on the need for new legislation as he mounted a weeklong push on criminal justice reform. A day earlier, Obama commuted the sentences of 46 nonviolent drug offenders — the most commutations a president has issued on a single day in at least four decades.

Upon arriving Tuesday in Philadelphia, Obama met with a number of former prisoners to discuss their experience re-entering society, the White House said. And on Thursday, Obama planned to put a personal face on the nation's mushrooming prison population with a visit El Reno Federal Correctional Institution outside of Oklahoma City — the first visit to a federal prison by a sitting U.S. president.

The assertive moves reflected a president eager to wield his executive power during his waning years in office to reduce harsh sentences, cut costs and correct disparities he said have disproportionally burdened minorities. Earlier in his presidency, as he spent his political capital carefully on major domestic priorities, Obama spoke cautiously and only intermittently about the need for smarter sentencing and other justice changes.

But as of late, public attention has been piqued by a serious of upsetting incidents across the country. In places like Baltimore, New York and Ferguson, Missouri, tensions between law enforcement and their communities have spilled out into the open, underscoring longstanding concerns among minority communities that they're treated differently in the criminal justice system.

Obama pointedly acknowledged that many people in the U.S. need to be in prison — "murderers, predators, rapists, gang leaders" — yet he said that in too many instances, law enforcement is treating young black and Latino men differently than their white peers.

"This is not just anecdotal. This is not just barbershop talk," he said.

The White House said Obama wouldn't hesitate to commute more sentences in the coming months if the circumstances were right. Yet Obama's ability to address the problem unilaterally is limited, as the White House readily concedes. So Obama has set his sights on the kind of comprehensive fix that only Congress can provide.

"The statistics cannot be ignored. We cannot close our eyes anymore," Obama said.

Working in Obama's favor: tentative but optimistic signs of common ground between Republicans and Democrats.

Republicans in particular have spoken with growing enthusiasm about the need for structural change. Senate Judiciary Committee Chairman Chuck Grassley, R-Iowa, has been working on legislation that could reduce some mandatory minimums. Republican Sen. John Cornyn of Texas and Democratic Sen. Sheldon Whitehouse of Rhode Island are backing a bill that would steer lower-risk inmates into programs where they could earn earlier release by participating in recidivism-reduction programs.

In another positive sign for the prospects of justice reform, a number of 2016 presidential candidates have taken an active interest in the issue. Sen. Rand Paul, R-Ky., has mounted a vocal push to restore voting rights to nonviolent felons who have served their terms and to make it easier for people with criminal records to get jobs. Gov. Chris Christie, R-N.J., planned to give a speech Thursday in the troubled city of Camden focusing on nonviolent drug offenders.

But not all Republicans were receptive to Obama's pitch. A group of 19 Republicans, led by House Judiciary Committee Chairman Bob Goodlatte of Virginia, wrote a letter Tuesday to Attorney General Loretta Lynch accusing Obama of blatantly usurping congressional authority and using his pardon power for political purposes.

Since Congress enacted mandatory minimum sentences for drug crimes, the federal prison population has multiplied, from just 24,000 in the 1980s to more than 214,000, according to Families Against Mandatory Minimums. In 2010, Obama signed the Fair Sentencing Act, cutting penalties for crack cocaine offenses. And last year, the independent Sentencing Commission reduced guideline ranges for drug crimes and applied those retroactively.