Significantly, her husband added a foreword in which he implicitly agreed that some of the policies he himself embraced two decades ago were too extreme. “The drop in violence and crime in America has been an extraordinary national achievement,” Bill Clinton wrote. “But plainly, our nation has too many people in prison and for too long — we have overshot the mark.”

In addition to Mrs. Clinton’s essay, the book, called “Solutions: American Leaders Speak Out on Criminal Justice,” scheduled to be released Tuesday, includes essays by two likely Democratic challengers, Mr. Webb of Virginia and former Gov. Martin O’Malley of Maryland. Republican contributors include Mr. Christie of New Jersey, Mr. Cruz and Mr. Perry of Texas, Mr. Paul of Kentucky, Mr. Rubio of Florida, Mr. Walker of Wisconsin and former Gov. Mike Huckabee of Arkansas.

Image Senator Ted Cruz of Texas said he wants to ease mandatory minimum sentences. Credit... Ian Thomas Jansen-Lonnquist for The New York Times

Also included is a recent speech from Vice President Joseph R. Biden Jr., who has positioned himself to run in 2016 if Mrs. Clinton falters. Former Gov. Jeb Bush of Florida was one of the few major candidates who did not participate; a spokeswoman for him had no comment, but he has signed on to a conservative group’s call for cost-effective alternatives to prison.

While crime has fallen in recent decades, the prison population has risen, although it has plateaued in recent years. More than 2.2 million Americans are behind bars, and a National Research Council study found that the state and federal prison population in 2009 was seven times what it was in 1973. Although the United States makes up less than 5 percent of the world’s population, it has more than 20 percent of its prison population.

The issue has been particularly acute among younger African-American men. Almost one in 12 black men from 25 to 54 are locked up, compared with one in 60 nonblack men in that age group. Many more have been released but have convictions on their records that make it hard to find jobs or vote.

The issue has drawn together an odd-bedfellows coalition of liberals and libertarians seeking bipartisan solutions. Mr. Paul has worked across the aisle with Senator Cory Booker, Democrat of New Jersey, and several other candidates have also been working in this area. In Texas, Mr. Perry diverted some drug offenders to treatment, generating praise from liberals and conservatives alike. Mr. Cruz has signed on to several pieces of legislation to change the system.