President Obama delivers a speech to the NAACP's 106th National Convention. (Video:

President Obama called for an overhaul of the criminal justice system Tuesday, saying that the United States needed to reevaluate an "aspect of American life that remains particularly skewed by race and by wealth."

The speech at the NAACP’s national convention, coming on the heels of a sweeping act of clemency Monday and ahead of his visit Thursday to a federal prison in Oklahoma, was the formal launch of one of the president’s last major legislative campaigns.

Sentencing reform represents one of the final domestic policies Obama hopes to broker on Capitol Hill before leaving office.

Telling the audience that “we can’t close our eyes anymore,” Obama noted that the nation’s prison population had more than quadrupled from 500,000 in 1980 to 2.2 million today.

“In far too many cases, the punishment simply doesn’t fit the crime,” he said. “And by the way, the taxpayers are picking up the tab for that price.” He argued that the $80 billion the federal government spends each year on prisons — nearly a third of the Justice Department’s budget — could instead fund preschool for every 3- and 4-year-old in the country.

Graphic: Here’s what America’s federal prison inmate population looks like

White House senior adviser Valerie Jarrett said in an interview that the issue was personal to the president, who has met regularly with young people of color and has spoken of how they face a less forgiving environment than he experienced growing up.

“He just wants to make sure they don’t get unfairly stuck in the criminal justice system because they’ve made mistakes early in their lives, without the ability to ever have a second chance,” she said.

Obama will become the first sitting president to visit a federal prison when he travels to El Reno, Okla., on Thursday. He said that he wanted to “shine a spotlight” on prison conditions and that those who are incarcerated “are also Americans,” even though they have made mistakes.

“And in the American tradition and in the immigrant tradition of remaking ourselves, in the Christian tradition that says none of us is without sin and all of us need redemption, justice and redemption go hand in hand,” he said. Before Tuesday’s speech he met with four ex-offenders — two black, one Latino and one white — who have rebuilt their lives since leaving prison.

The president outlined reforms he hoped would foster change “in the community, in the courtroom and in the cellblock.”

“For nonviolent drug crimes, we need to lower long mandatory minimum sentences — or get rid of them entirely,” he said.

He said he had ordered Attorney General Loretta E. Lynch to start a review of the use of solitary confinement, adding that the country had to do more to combat poor conditions in prisons and prepare those inside to re­enter society.

Tuesday’s civil rights conference represented a gathering of more than 3,000 of the president’s most committed supporters. When the doors opened at 2 p.m., two hours before Obama’s speech, many attendees ran toward the front. Several minutes later, as Pennsylvania Gov. Tom Wolf (D) prepared to speak, an announcer boomed into the microphone, “Ladies and gentlemen, can you please take your seats? Not everybody can sit in front.”

But Obama’s message was aimed as much at conservatives outside the hall as at the audience inside the room. A growing number of groups and politicians on the right have taken up the cause of criminal justice reform as a way to save taxpayer dollars and curb recidivism

Marc Levin, who directs the Right on Crime initiative at the Texas Public Policy Foundation, noted that conservative states, including Alabama, Georgia, Nebraska, South Carolina, Texas and Utah, had adopted sentencing reforms in recent years. In January 2007, the Texas legislative budget board predicted that the state would have to spend “a few billion dollars” on providing 17,000 additional prison beds over the next five years, Levin said; later that year, lawmakers approved $241 million on treatment services as well as drug courts and halfway houses.

Georgia has passed drug sentencing reforms for three sessions in a row. California voters adopted a ballot proposition in the fall making "non-serious, non­violent crimes" misdemeanors instead of felonies unless the offender has specific previous convictions; under the measure, the money that will be saved by these changes will go to for mental health and drug treatment, education and victim compensation.

Lenore Anderson, who co-authored Proposition 47 and serves as executive director of Californians for Safety and Justice, said that voter attitudes had shifted decisively on the issue and that the goal of the proposition was that “we could finally put the nail in the coffin that the only way to talk about criminal justice was with a ‘tough on crime’ lens.”

In recent months, Obama and his top aides have held a handful of private meetings aimed at laying the groundwork for a compromise bill on sentencing reform. In late February, Obama brought 16 senators and House members to the White House to discuss general principles. And on April 16, Koch Industries' general counsel Mark Holden, who is working with officials from other foundations through a group called the Coalition for Public Safety, met with Jarrett, White House domestic policy director Cecilia Muñoz and White House counsel W. Neil Eggleston on the issue.

But until Tuesday, the president had not spelled out specifically what he expected to see in a bill, leaving the task to lawmakers.

After holding nearly a year and a half of field hearings, Reps. F. James Sensenbrenner Jr. (R-Wis.) and Robert C. "Bobby" Scott (D-Va.) introduced the Safe, Accountable, Fair and Effective (SAFE) Justice Act late last month, a comprehensive measure that would impose mandatory minimum sentences on higher-level drug traffickers rather than low-level offenders; apply life sentences for drug trafficking only in extreme cases; and allow eligible offenders to petition for re­sentencing under new trafficking laws.

Senate Judiciary Committee Chairman Charles E. Grassley (R-Iowa) said Tuesday that lawmakers on his panel are likely to offer a bipartisan bill soon.

Sen. Patrick J. Leahy (Vt.), the top Democrat on the Judiciary Committee, issued a statement Tuesday after the president’s speech suggesting that when it comes to criminal justice reform, “there has been enough talk.”

“The question now is whether we have the leadership in Congress to act and pass the meaningful reforms that our country urgently needs,” Leahy said. “Our wrongheaded approach to criminal justice is breaking the bank and making us less safe.”

Sari Horwitz in Washington contributed to this report.