The task of many a campaigner is to persuade the public his opponents have a history of horrors, and the reality of many an election is that all mutual allegations are correct.

The criminal justice portion of the Democratic primary debate Wednesday night produced just such a scenario, with front-runner former Vice President Joe Biden and top five contender Sen. Kamala Harris (D-Calif.) coming under particular scrutiny.

It's a scrutiny both deserve, as they each now proclaim positions that stand in stark contrast to their careers thus far. That's not to say real evolution on this issue is impossible — and I'll say more on sincere growth vs. calculated flip-flops in a moment — but it is to say such an evolution, for these two, demands proof. The blows they sustained from Sen. Cory Booker (D-N.J.) and Rep. Tulsi Gabbard (D-Hawaii) hit hard because they were backed by indisputable records of expansion of the martial and carceral state.

Biden and Booker were the first to get into it in Detroit on Wednesday. "We have a system right now that's broken," Booker charged. "And if you want to compare records — and frankly, I'm shocked that you do — I am happy to do that. Because all the problems that [Biden] is talking about, that he created ... that you were, frankly — to correct you, Mr. Vice President — you were bragging, calling it the Biden crime bill, up until 2015."

Booker's own record on criminal justice isn't flawless, as Biden was quick to retort. But in terms of large-scale expansion of mass incarceration, over-criminalization, and even policing for profit, Biden remains firmly in the lead. It is no exaggeration to say his present platform on these issues is a bold stance against many of his own unjust accomplishments, nor is Booker wrong that Biden's about-face is so recent he's still spinning.

The last time Biden ran for president, in 2008, his campaign website boasted of his support for the 1994 crime law and did indeed brand it the "Biden Crime Law." In 2016, he touted his work drafting the bill and claimed that "by and large what it really did [was] it restored American cities." And during the Wednesday debate, the Biden campaign tweeted a partial defense of the legislation which conveniently neglected to mention its many, many provisions that are rightly unpopular today.

Biden "was really pivotal in leading the Senate in worsening all of the provisions of" the 1994 law, "which expanded the death penalty and created new mandatory minimum sentences," Princeton political scientist Naomi Murakawa explained to the Marshall Project in a 2015 interview. "Biden was truly a leader and worked very closely and very happily with conservative senators just to bid up and up and up," she added, explaining how he led the way to "really deeply disturbing, dangerous reforms that have made the criminal justice system more lethal and just bigger." His 2020 criminal justice agenda is a big improvement over positions past, but many criminal justice reformers are understandably unimpressed if not unconvinced.

Then there's Harris, who came prepared for a fight with Biden and instead found herself skewered by Gabbard in perhaps the most notable moment of the night.

I want to bring the conversation back to the broken criminal justice system that is disproportionately negatively impacting black and brown people all across this country today. Now Sen. Harris says she's proud of her record as a prosecutor and that she'll be a prosecutor president.

But I'm deeply concerned about this record. There are too many examples to cite but she put over 1,500 people in jail for marijuana violations and then laughed about it when she was asked if she ever smoked marijuana. She blocked evidence that would have freed an innocent man from death row until the courts forced her to do so. She kept people in prison beyond their sentences to use them as cheap labor for the state of California. And she fought to keep a cash bail system in place that impacts poor people in the worst kind of way. [Rep. Tulsi Gabbard via NBC News]

Gabbard ended a brief rebuttal statement with a demand that Harris apologize to "the people who suffered under [her] reign as prosecutor." That's exactly what Harris has been unwilling to do. "She says all the right things  —  frankly, all the right platitudes  —  about criminal justice reform," Robert Weisberg of Stanford Law School told The California Sunday Magazine. "But she tends to lead from behind and wait until she sees the conventional wisdom solidifying."

Harris' position is admittedly difficult as a matter of political strategy. As I've written in a previous examination of her record as a prosecutor, explicitly repudiating her old policies risks undermining the political value of years of public office, and publicly proclaiming one's own past failure of ethics, conviction, or judgment is never pleasant.

But for Biden and Harris alike, the repudiation matters. It's not enough to do the usual "it was a long time ago; times have changed and so have I" song and dance on criminal justice. If that's the approach these two are determined to take — well, then Biden does seem, as former HUD Secretary Julian Castro charged Wednesday, to have "flip-flopped on these things" when it became politically convenient to do so. And it means Harris, as her critics have said, is a cop: "someone who will always defer to authority and the status quo, someone who is unaccountable and not to be trusted."

Sincere growth on an issue where one's old errors continue to have measurable, destructive effects on people's lives requires more than trotting out a shiny new platform. The past requires a reckoning, not a rebranding. Criminal justice reformers often extol the virtues of redemption and might be willing to offer it to these two, but first they would have to repent.