WASHINGTON - Sen. Cory Booker has found a signature issue.

The New Jersey Democrat has become one of the most vocal and visible advocates for reforming the way the criminal justice system hands out sentences and treats people after they leave prison.

After keeping a low profile early in his Senate tenure, Booker has added his voice to a sprawling coalition that includes would-be presidential candidates on the right such as Sens. Rand Paul (R., Ky.) and Ted Cruz (R., Texas); two of the most senior liberal voices, Sens. Richard Durbin (D., Ill.) and Patrick Leahy (D., Vt.); and tea party champions such as Sen. Mike Lee (R., Utah) and Rep. Raul Labrador (R., Idaho).

President Obama is on board, too. Booker was one of more than a dozen Democrats and Republicans who met with him at the White House on Tuesday to discuss potential changes.

"There's a historic moment brewing," Booker said later, citing support across the political spectrum and a change in the national consciousness.

"This is what we're working on every single day," he said in his office after the White House meeting.

The senator was accompanied by a new staff lawyer hired to focus on the issue.

Booker then rushed to a live Huffington Post interview on the reform effort, and the next day he promoted the cause with Lee on a Salt Lake City radio show and with Paul in an interview with Yahoo's Katie Couric.

This week, the National Council of La Raza, a Hispanic advocacy group, will honor Booker for his work on the subject.

Advocates for change, citing the moral and financial costs of a growing prison population, hope to reduce mandatory minimum sentences, improve the treatment of inmates, and open more opportunities once prison sentences end.

From right to left

An unusual alliance of advocacy groups has joined in. It includes the conservative activist Koch brothers; the antitax outfit led by Grover Norquist, Americans for Tax Reform; and the liberal Center for American Progress and American Civil Liberties Union, among others.

Singer John Legend spoke out on the issue after winning an Oscar.

For Booker, the cause offers a chance to find a niche in Congress less than two years after entering the Senate, to uphold his pledge to work across the aisle, and to have a hand in one of the rare issues on which significant action looks possible.

He was one of the "all-time stars" at the White House meeting, said Leahy, the Senate's longest-serving member.

"He speaks about the real effect on real people," Leahy said, "not just numbers."

In black and white

In a speech on the Senate floor Thursday, Booker said he was driven by the disparities in the treatment of people who use drugs such as marijuana in places such as his hometown, suburban Harrington Park, N.J., and the elite universities he attended, Stanford and Yale, compared with those in the poor, largely minority city where he was mayor, Newark.

"The justice system they experienced for breaking the law was very different from the justice system I saw in Newark," he said.

Whites and blacks use marijuana at similar rates, Booker said, but blacks are arrested more than three times as often. One federal report found that African American men face sentences 13 percent longer than white men for drug crimes.

Most prominently, Booker and his allies say the United States has 5 percent of the world's population but 25 percent of its prisoners.

There are several proposals to change the system.

The most ambitious focuses on "front end" changes at sentencing. The Smarter Sentencing Act would cut mandatory minimum sentences and expand the pool of people eligible for lesser sentences at judges' discretion.

A version introduced last year would save $3 billion over a decade as 250,000 people would be released from prison earlier than expected, according to the nonpartisan Congressional Budget Office.

Booker and Paul have also teamed to propose "back end" changes they hope would open opportunities for those leaving prison.

Their "Redeem Act" would seal or expunge criminal records for nonviolent juvenile offenders and offer a path for nonviolent adult convicts to seal their records.

Others have proposed laws that would allow early release for good behavior.

But it is unclear what package can both gain consensus support and clear Congress, and significant obstacles remain.

The chairman of the Senate Judiciary Committee, Charles Grassley (R., Iowa), has opposed sentencing changes and could block a bill.

In a February floor speech he accused those seeking changes of peddling "myths" that exaggerate the impact of mandatory minimum sentences and warned that changes could reduce penalties for heroin-related offenses and lead to milder sentences for ISIS terrorists who sell drugs.

"If we are informed by facts," Grassley said, "we will not make unwise and dangerous changes to our federal sentencing laws."

A prosecutors' organization wrote key lawmakers last year arguing that mandatory minimums reduce crime, give authorities leverage to force criminals to cooperate, and provide consistency in sentencing.

"Most importantly," said the National Association of Assistant United States Attorneys, mandatory minimums "protect our citizens."

Booker hopes to overcome those objections as early as this year.

The cause has something for all sides of the political aisle:

Civil-liberties advocates and religious leaders make arguments for offering second chances, liberals raise concerns about unequal treatment, libertarians see a chance to roll back what they consider heavy-handed government rules, and fiscal conservatives hope to cut the cost of imprisoning low-level offenders.

Paul has said corrections spending cost each American $77 a year in 1980, but $260 by 2010.

Free to ski

Booker, speaking on the Salt Lake City radio show with the conservative Lee, played up the religious argument and called it "stupid" to use taxpayer dollars "to warehouse people for far longer than it takes to rehabilitate them."

The money, he added, would be better spent on infrastructure "so I can drive to Utah and ski."

Booker's talent for playing to all audiences has given him a reach far beyond the typical political crowd, making him a valuable booster as advocates try to build support.

(In the last three months he has appeared in the star-studded Colbert Report finale, the premiere of Comedy Central's The Nightly Show With Larry Wilmore, and in a Parks and Recreation cameo.)

And he, of course, has his famous Twitter account.

One tweet Thursday summed up his recent efforts. Quoting Gandhi, Booker wrote: "Action expresses priorities."