Parisa Tafti became a lawyer because a college friend was wrongly found guilty of rape, a conviction that was overturned five years later. Over the past two decades she has sought to get other innocent people out of prison by challenging the work of prosecutors. Now she wants to become one.

Tafti has launched a Democratic primary campaign to unseat Arlington County Commonwealth’s Attorney Theo Stamos, a prosecutor for the past 30 years.

The clash is part of a national criminal justice reform movement that has come to Northern Virginia and could radically reshape law and order in Arlington, Fairfax and Loudoun. In all three counties, liberal challengers are taking on prosecutors whose views they see as retrograde and excessively punitive.

“I think there’s a lot of frustration with the lack of progress on criminal justice reform both in the country and in the commonwealth,” said state Sen. Scott A. Surovell (D-Fairfax). “A lot of people in the reform community think prosecutors should exercise their discretion in cases more.”

Unlike the incumbents, the challengers are promising to stop prosecuting simple marijuana possession, to refuse to request cash bond for defendants awaiting trial and to not seek the death penalty.

“The American criminal justice system is now a mass incarceration machine set on auto-pilot,” Tafti said in a statement announcing her run. “As a public defender, I know all too well how this machine dismantles communities, destroys families, uses bad science, and wastes money.”

She pointed to statistics showing black people make up less than 10 percent of Arlington’s population but two-thirds of its jail inmates.

In neighboring Fairfax County, incumbent top prosecutor Raymond F. Morrogh (D), who ran unopposed in the past two elections, faces a challenge from a former federal prosecutor and Army helicopter pilot. Steve Descano calls his run a “values campaign.”

“The most important thing is we have to bring Fairfax County values to office,” Descano said. “I don’t think we have that in Fairfax County right now.”

Like Tafti, he criticized his opponent for signing on to a 2016 brief that denounced the move by then-Gov. Terry McAuliffe (D) to restore voting rights to more than 200,000 felons as too broad. Both challengers want to expand alternatives to prosecution for drug addicts, the mentally ill and teens.

Morrogh and Stamos say they are reformers — within a complex system where victims also have rights.

“It’s interesting that she describes herself as an ‘Innocence Protection Attorney,’ as that is what I’ve been engaged in for more than thirty years,” Stamos said of Tafti in a statement.

While Stamos recently announced that she will no longer seek cash bail for most minor misdemeanors, she argued that it is an important tool to ensure people show up for court in more-serious cases. On that and other issues, she argued that state law prevents the kind of dramatic change Tafti and other challengers seek.

“If she wants to decriminalize marijuana, she should go to Richmond,” Stamos said in an interview. “Unless and until these laws on the books are repealed, I don’t think it’s the appropriate exercise of prosecutorial discretion to usurp the will of the legislature.”

Morrogh, who has also been a prosecutor for over 30 years, said he was “progressive before progressive was cool.” He noted that he worked to help establish a veterans court, drug court and mental-health court in Fairfax County, as well as efforts to divert the mentally ill charged with crimes into treatment instead of jail.

He said he heavily uses a program that places defendants in pretrial supervision rather than asking for bond. But he also said those concerns should be balanced with victims’ rights.

“I have a vast amount of experience trying the most complicated criminal cases,” Morrogh said.

The race for commonwealth’s attorney in Loudoun County will pit incumbent Republican Jim Plowman against a Democratic challenger in November. Buta Biberaj is the only Democrat to have entered the race.

Plowman, who is in his fourth term, swept into office in 2003 promising a traditional tough-on-crime approach. He said crime in Loudoun County has dropped each of the past five years, making it one of the safest communities in the area.

“During my tenure we’ve continued to hold violent and repeat offenders accountable, seeking fair and just resolutions for victims and the community,” Plowman wrote in an email.

Biberaj, a 25-year trial lawyer and former substitute judge, said on her campaign website that she would take the office in a different direction, focusing on bond reform and pushing treatment for the addicted and mentally ill instead of jail. She did not respond to requests for comment.

Lawyers and political watchers are also waiting to hear whether Prince William County Commonwealth’s Attorney Paul B. Ebert (D) runs again. Ebert, who has held office for 50 years and has sent more people to death row than any prosecutor in Virginia’s history, would be seeking his 14th term.

Ebert is an institution in Prince William but has faced criticism in recent years after a federal judge overturned one of his high-profile capital convictions and death-penalty sentences, saying his office had withheld key evidence from the defense.

Ebert is expected to face a challenger if he runs. He did not respond to requests for comment.

Rick Conway, Ebert’s chief deputy, said his boss and other incumbents are “open to discussion concerning criminal justice reform” and have advocated for some changes. But “when you’re talking about your head prosecutor of your jurisdiction,” he said, “you want somebody who believes in law and order and understands that we don’t make the laws — we’re charged with enforcing them.”

It is too early to say whether the challengers will be competitive, but they may take heart from the surprise November victory of Democrat Scott Miles who beat Chesterfield’s chief deputy Commonwealth’s Attorney. Republican John Childrey had been endorsed by the longtime Republican incumbent, who retired over the summer.

Across the country, groups associated with George Soros, the liberal philanthropist, and members of the Black Lives Matter movement have spent millions in dozens of local races, helping elect progressive prosecutors in Philadelphia, Chicago, St. Louis and other cities.

Tafti and Descano said they had not received similar funding to date.

An earlier version of the story incorrectly identified the position of the Republican opponent in the November race for Chesterfield County Commonwealth’s Attorney. John Childrey was the chief deputy Commonwealth’s Attorney.

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