Republican presidential candidate Donald Trump talked about how he would fight New Hampshire's heroin "problem" the day after Fox Business Network's debate. He's one of several candidates to weigh in on the issue of drug addiction. (Sarah Parnass/The Washington Post)

More than 40 years after Republican President Richard M. Nixon coined the phrase “war on drugs,” many GOP presidential candidates are calling for an end to one of its central tenets — by agreeing with Democrats to treat low-level drug offenders rather than incarcerate them.

The Republicans are selective, however, about who is deserving of their compassion.

Several GOP presidential contenders have advocated treating the nation’s growing heroin epidemic as a health crisis, not a criminal one. But most stop short of advocating the same approach to other drug laws, notably those involving marijuana and crack cocaine, which disproportionately affect African Americans.

Such views highlight the resonance and reach of the opiate epidemic — but also a persistent racial and geographic divide in American politics. The heroin epidemic has overwhelmingly hit whites. It has also skyrocketed to the top of voters’ lists of political priorities in the same bands of America — rural states, the suburbs and notably the early voting state of New Hampshire — that track directly with where Republicans must perform well to win back the White House next year.

New Jersey Gov. Chris Christie, for instance, regularly compares the moral imperative to treat drug addicts with rehabilitation to cancer treatments for smokers like his mother.

New Jersey Gov. Chris Christie, center, regularly compares the moral imperative to treat drug addicts with rehabilitation to cancer treatments for smokers like his own mother. (Daniel Acker/Bloomberg)

“No one came to me and said, ‘Don’t treat her; she got what she deserved,’ ” Christie told a small group of voters in New Hampshire. “We need to start treating people in this country, not jailing them.”

Yet Christie and most other GOP candidates have distanced themselves from broader criminal justice reforms that could be construed as “soft” on crime. They have not vocally endorsed similar proposals to reform marijuana punishments, which disproportionately affect African Americans. Nearly all of the candidates have been silent on racial disparities in criminal penalties for other nonviolent drug crimes.

The candidates are walking a narrow but perhaps politically astute line, some say, between making inroads with the ballooning number of suburban and rural voters who have been touched by the country’s exploding heroin crisis — yet not alienating Republican voters who fear that the roiling national debate about race and policing has left law enforcement exposed.

“Just because you have a smart approach to dealing with the heroin epidemic does not mean that you have to be soft on crime,” said Dave Carney, a GOP strategist in New Hampshire, where the candidates have spoken most forcefully about providing new assistance for heroin addicts. “Respect for law enforcement in our party is a winning issue every day of the week — and twice on Sunday.”

The rate of heroin deaths nearly quadrupled nationwide in a decade. Its growth has primarily happened outside of cities; according to one study, in the past decade, 90 percent of people who tried heroin for the first time were white, and 75 percent lived in the suburbs. In contrast, roughly half of new users in the 1970s were white, and half were black.

That may help explain why, even on issues in which there is growing conservative support — such as eliminating the sentencing disparity for crack and powder cocaine users or eliminating mandatory minimum sentences — GOP candidates have been hesitant to weigh in.

Former Arkansas governor Mike Huckabee responded dismissively to growing concerns about the racial disparities that stronger crack sentences have produced, noting that those sentences were initially advocated by black community leaders concerned about the crack cocaine epidemic in cities in the 1980s.

Sen. Marco Rubio of Florida, writing about mandatory minimum sentences, warned in an essay for the Brennan Center for Justice this year that “reductions in sentences for drug crimes should be made with great care.” And retired neurosurgeon Ben Carson was the only GOP candidate in attendance at a criminal justice forum on Saturday, where he voiced support for ending mandatory minimum sentences.

According to Grover Norquist, president of Americans for Tax Reform, candidates have been slower to talk about broader criminal justice issues from a conservative perspective not because they are hostile to the idea, but because primary voters themselves are focused on a narrow set of issues — including, recently, the growing heroin epidemic.

“When you’re running for office, you talk to people about things they already know. This is not a time to educate the electorate,” Norquist noted, adding that, for example, the crack cocaine and powder cocaine discrepancy is not an issue most Republican voters are knowledgeable about. “If I thought they were hostile and indifferent [to criminal justice reforms], I’d be concerned.” Norquist noted.

Nationally, the two parties are proceeding along separate and parallel paths on criminal justice reform. Forced to do so in part by the Black Lives Matter movement, each of the Democratic candidates has proposed detailed plans that address a wide range of drug and incarceration reforms. Republicans have focused their compassionate message on heroin but are more split on marijuana arrests and other reforms.

Christie has stopped short of supporting similar reforms when it comes to marijuana arrests, which overwhelmingly affect African Americans.

According to the American Civil Liberties Union of New Jersey, as governor, Christie presided over a 12 percent increase in petty arrests for marijuana possession, which disproportionately affect minority, urban offenders even though whites use the drug at similar rates.

“There’s a huge disparity in how Christie is sort of viewing drug reform or drug rehabilitation or providing those medical services or those other types of services to people who use heroin, which overwhelmingly are white middle-class people in New Jersey,” said Newark activist Rashawn Davis. “It’s young African American men like myself who suffer disproportionately from marijuana arrests in New Jersey.”

Christie spokeswoman Sam Smith said Christie’s support for reducing sentences for nonviolent drug offenders encompasses marijuana offenders. She said marijuana possession arrests in New Jersey “simply do not result in lengthy periods of incarceration” and that “often” they result in no incarceration at all. Simple marijuana possession charges in the state carry maximum penalties between six and 18 months.

Not every Republican candidate has drawn a line rhetorically with marijuana.

Most others, including Sen. Ted Cruz (R-Tex.), Rubio, former Florida governor Jeb Bush, Carly Fiorina, Huckabee and Ohio Gov. John Kasich, say they oppose legal recreational use — but they have taken a federalist approach by suggesting that the debate should be decided by the states.

Others, such as libertarian Sen. Rand Paul (Ky.), have been more willing to address the role of marijuana arrests in the country’s expensive incarceration system.

Paul also has taken a more sympathetic approach to the Black Lives Matter movement, saying that he supports “most” of the criminal justice changes that protesters have advocated. And he acknowledged that blacks are disproportionately affected by aggressive enforcement of marijuana laws and the racially skewed “disparity in sentencing in between crack cocaine and powder cocaine.”

Except for Paul’s appeal to libertarian purists — and younger voters on college campuses (including those at historically black universities) — the Republican field’s positions match a challenging 2016 political map in which they must solidify support among white voters in the nation’s rural and suburban swaths. Democrats, meanwhile, are expected to hold or expand their dominance among urban and minority voters.

According to Carney, who has worked for more than 35 years in Republican primary politics in New Hampshire, the first time that drug-related crime logged in as a top-10 issue among voters was in April — around the same time that heroin deaths topped traffic fatalities in the state. That’s one reason New Hampshire voters have been hearing more and more Republican candidates address the issue of drug addiction in sympathetic terms.

“The problem of heroin in New Hampshire is unbelievable,” businessman Donald Trump told a crowd in Manchester.

“It’s a horrible disease,” said Cruz, who has addressed addiction on CNN, speaking about the death of his half-sister.

Guarding against the risk of being seen as soft on crime, Christie joined other candidates in speaking out against the Obama administration’s release of 6,000 nonviolent drug offenders whose sentences were reduced under new sentencing guidelines — though he supports reducing sentences for nonviolent drug offenders.

Former Massachusetts governor Michael Dukakis (D), whose 1988 presidential ambitions were halted by political attacks tied to his support for a weekend prisoner furlough program, noted that “it’s always a risk” for politicians to support releasing prisoners.

“I applaud the fact we’re finally getting a bipartisan consensus on reform,” he said. “But unless we’re doing a much better job of training people or treating addiction in prison, some people are going to come out unready for what they’re facing.”

David Weigel contributed to this report.