U.S. Presidential candidate and Republican Senator of Florida Marco Rubio (L) greets attendees during a campaign event in Ankeny, Iowa, April 25, 2015. REUTERS/Jim Young

Sen. Marco Rubio (R-Fla.), like several other presidential aspirants, calls for criminal justice reform in an essay published in a newly released book put together by the Brennan Center for Justice. But where some of his Republican rivals have been bullish on dramatically reforming drug laws, Rubio isn't.

In the book, titled "Solutions: American Leaders Speak Out on Criminal Justice Reform," Rubio calls for cataloguing crimes and weeding out unnecessary laws, among other policy solutions -- but he sounds a careful note when it comes to revamping drug laws (all bolding below is ours):

There is an emerging consensus that the time for criminal justice reform has come. A spirited conversation about how to go about that reform has begun. Unfortunately, too often that conversation starts and ends with drug policy. That is an important conversation to have. But when we consider changing the sentences we impose for drug laws, we must be mindful of the great successes we have had in restoring law and order to America’s cities since the 1980s drug epidemic destroyed lives, families, and entire neighborhoods. I personally believe that legalizing drugs would be a great mistake and that any reductions in sentences for drug crimes should be made with great care.

Compare that to what Sen. Rand Paul (Ky.) wrote in his essay:

The War on Drugs is principally responsible for the wide gap in confidence between minorities and the police. African Americans use drugs at roughly the same rate as whites, but are more than twice as likely as whites to be arrested for drug possession. Harsh mandatory minimum sentencing laws have also contributed to fatherlessness in these communities. From 1980 to 2000, the number of children with fathers in prison rose from 350,000 to 2.1 million.

Or Sen. Ted Cruz (Tex.):

Harsh mandatory minimum sentences for nonviolent drug crimes have contributed to prison overpopulation and are both unfair and ineffective relative to the public expense and human costs of years-long incarceration.

Here's former Arkansas governor Mike Huckabee, who is considering a run:

An Arkansas prison official once told me that 88 percent of incarcerated inmates at his prison were there because of a drug or alcohol problem or because they committed a crime in order to get drunk or high. As he astutely observed, we do not have a crime problem, we have a drug and alcohol problem. While those who deal drugs and entice others into enslaving addictions deserve serious time and tough sentences, we lock up many nonviolent drug users, some of whom spend longer periods in prison than they would if they had committed a violent crime. Though many of the efforts to address this problem have brought some measure of sanity to the process — drug treatment as opposed to merely warehousing drug users — we need to do things differently.

And former Texas governor Rick Perry, another Republican weighing a bid:

By [offering] treatment instead of prison for those with drug and mental health problems — upon entrance and exit from prison — the United States can eliminate our incarceration epidemic.

None of this is to say that there is no overlap between Rubio's plan and plan offered by other Republicans. There is.

But Rubio's cautious approach to revamping drug laws compared to the heavy emphasis others have placed on changing them illustrates how there is some notable daylight between the Republican candidates -- on an issue where, on the surface, they are all aligned.

Perhaps most notable is the contrast between Rubio and Paul, who has made his critique of both the "War on Drugs" and mandatory minimum sentencing a central plank of his political platform.

The Republican candidates for president hold very similar views on a lot of issues. But it's not all overlap.