Hillary Clinton has had a long time to think about the death penalty, going back to her her days as a criminal law professor in the 1970s. But public and private comments she's made over the years suggest she's never quite fully come to terms with whether to support it.

Clinton's comments in a CNN town hall Sunday are some of her most definitive yet about where the Democratic presidential front-runner stands on this quintessential issue. On Sunday, Ricky Jackson of Ohio, a former death-row inmate who was exonerated after 39 years for a crime he didn't commit, asked her how she can support the death penalty when it threatens the lives of innocent people like him.

Clinton replied it's "a profoundly difficult question." She said she's skeptical of the states' abilities to dole out the death penalty fairly, but she explained she can't rule the death penalty out entirely for specific cases at the federal level -- like the Oklahoma City bombing. She went on:

Where I end up is this: Given the challenges we face from terrorist activities primarily in our country that end up under federal jurisdiction, for very limited purposes, I think it can still be held in reserve for those. ... But a very limited use of it in cases where there has been horrific mass killings. That's really the exception that I still am struggling with. And that would only be in the federal system.

Her comments come as the nation is trying to retool the way it approaches criminal justice reform after a tough-on-crime era under Clinton's husband in the 1990s led to high incarceration rates with racial disparities. Many prominent liberals, including Clinton's opponent, Sen. Bernie Sanders (I-Vt.), wants to abolish the death penalty, and conservative-leaning states like Nebraska and Utah are even considering or have considered getting rid of it.

Through it all, Clinton has said relatively little about her nuanced position, which appears to have evolved over the years along with the nation's -- some would say subtly, others would argue more dramatically. We would argue her position on the death penalty has been much more consistent over the years than her position on trade. But because she's said so little on it, it's even harder to suss out just how much (or how little) her positions on the death penalty have changed.

Here's a brief history of Clinton's relationship to the death penalty, put together in part thanks to a thorough review of her entire history on criminal justice via The Marshall Project:

While her husband was in office, she "agonized" over his positions 

The Clintons in 1992 (AP Photo/Greg Gibson, File)

Bill Clinton's desire to appear tough on crime -- since the days he lost reelection as governor of Arkansas after being attacked as too soft -- seems to have guided his wife's public positions on the death penalty, at least while he was in office.

When Clinton was a professor of criminal law in the 1970s, she headed a legal aid clinic at the University of Arkansas. There, her team helped save the life of a mentally impaired black man sentenced to death by an all-white jury. But Clinton left her name off the amicus brief her team filed to save the life of Henry Giles. The Marshall Project notes her husband was running for attorney general in Arkansas at the time.

While her husband was president, she lobbied for two tough-on-crime bills he signed that, among other things, expanded the kinds of federal crimes eligible for the death penalty and placed time limits on death penalty appeals.

But there's evidence to suggest she was conflicted with her husband's stance. In a 2007 book "God and Hillary Clinton: A Spiritual Life," Clinton's spiritual mentor tells author Paul Kengor she "agonized" over her husband's support for the death penalty.

In the Senate, she was an "unenthusiastic" supporter of the death penalty 

Sen. Clinton in 2006 (Mark Wilson/Getty Images)

When Clinton had the opportunity to comment as a politician in her own right on the death penalty, she caused a stir on the left. In her 2000 Senate race, Clinton said the death penalty had her "unenthusiastic support" (supporting the death penalty was officially part of the Democratic Party's platform until 2004).

Washington Post columnist Richard Cohen said at the time that Clinton didn't "have the guts to oppose capital punishment." Writing in the New York Observer, journalist and author Ron Rosenbaum called her Senate campaign " a disaster" for liberalism, citing in part her support for the death penalty and accusing Clinton of pandering to voters. The New York Observer's editorial board said she supported a "barbaric solution."

Despite the drama, when Clinton got to the Senate, she largely stayed out of the debate on criminal justice. The Marshall Project reports she signed onto a handful of mostly failed bills to reform criminal justice.

One of those specifically mentioning the death penalty was the Innocence Protection Act, which aimed to reduce the chance a person gets wrongfully sentenced to death in part by expanding and helping pay for DNA testing for people sentenced to the death. It took a few years, but President George W. Bush signed it into law in 2004.

On the presidential trail, she eases into her current position 

(Photo by Scott Olson/Getty Images)

More years went by without Clinton explicitly addressing how she feels about the death penalty. In her first run for president in 2008, when she was still a senator, she called for "a thorough review of all the penalties" for the 1994 crime bill she supported and her husband signed into law. News stories from the 2008 campaign describe her as a "firm" or "staunch" supporter of the death penalty.

But she appeared to soften her stance during her second bid for the White House. In an October event in New Hampshire, she responded to a question about her position and had this to say, via MSNBC:

We have a lot of evidence now that the death penalty has been too frequently applied, and too often in a discriminatory way. I do not favor abolishing it, however, because I do think there are certain egregious cases that still deserve the consideration of the death penalty. But I’d like to see those be very limited and rare, as opposed to what we’ve seen in most states.

She expand on her view-- that the death penalty should be reigned in but not abolished entirely -- Sunday.

But really, Clinton has said so little on the death penalty over the years, it's difficult to gauge just how drastically (or not) her position has changed. As evidenced by her use of words like "struggled" when she does talk about it, it seems whatever conclusions she's come to have not been easy for her.