Should the surviving Boston Marathon bomber be allowed to vote from prison? It sounds like an easy question, but it wasn’t for California Sen. Kamala Harris at a CNN town hall April 22. “I have been long an advocate of making sure that the formerly incarcerated are not denied a right to vote,” she answered. When host Don Lemon tried to pin her down on whether Dzhokhar Tsarnaev should be allowed to vote, she said: “I think we should have that conversation.”

The next day she changed her mind. After saying at a press conference that the question was “complex” and she planned to “talk to experts” about it, she added: “Do I think that people who commit murder, people who are terrorists should be deprived of their rights? Yeah, I do. I’m a prosecutor.”

It won’t be the first awkward flip-flop for Ms. Harris, who served six years as California’s attorney general before her election to the Senate in 2016. Already her experience as the state’s top law-enforcement officer is proving to be stumbling block in the presidential nomination contest for a party increasingly antagonistic toward police, traditional norms and the justice system.

When Ms. Harris ran for San Francisco district attorney in 2003, she positioned herself as tough on crime, a more reasonable alternative to the extremely progressive incumbent, Terence Hallinan. She won with support from police, victim advocates and even Republicans. But she disappointed them a few months after taking office by refusing to pursue the death penalty for a man who killed San Francisco police officer Isaac Espinoza. In 2008 she made a show of deliberating for months before deciding not to seek the death penalty for MS-13 gang member Edwin Ramos, who was convicted of a triple murder.

Now that Ms. Harris has set her sights on the White House, she’s been distancing herself from other, tougher aspects of her record as district attorney and attorney general. She cracked down on truancy by criminally prosecuting 25 parents; now she plays down the effort by insisting that “no one went to jail.” She once scoffed at decriminalizing prostitution; she now supports it. As district attorney, she worked to increase bail in San Francisco; she now favors the abolition of bail in favor of computerized risk-assessment programs—although many progressive activists have derided those as racially biased.