Boston Mayor Michelle Wu endorsed City Councilor Ricardo Arroyo for Suffolk County District Attorney over the weekend, prompting the campaigns for Arroyo and his rival, interim DA Kevin Hayden, to directly criticize one another for the first time since joining the race to succeed now-U.S. attorney for Massachusetts Rachael Rollins.

“If Mayor Wu believes a novice attorney with zero public safety experience should be the top law enforcement officer in the county, that’s her choice,” said Adam Webster, a spokesperson for Hayden’s campaign after Wu’s endorsement. “We’re confident that voters will disagree.”

On Monday, Arroyo’s campaign issued a statement blasting the sitting DA’s campaign.

“This is a desperate attack from an appointed official who is rolling back the progressive reforms that were overwhelmingly voted for when Suffolk County elected Rachael Rollins,” said Mohammed Missouri, campaign manager for Arroyo in a statement to GBH News. “Councilor Arroyo has represented hundreds of people in his career as a Public Defender and that experience is what drives his vision for a more just system that reduces crime while addressing rampant disparities.”

Arroyo’s endorsement from Wu, which comes with the power of a Boston progressive base that vaulted her to the mayor’s seat by a nearly 2-to-1 margin, deepens his credibility as Rollins’ progressive heir, a posture the two-term city councilor has embraced since launching his bid for the DA seat in February.

Hayden, a Democrat and first-time candidate for public office, has shirked political labels and candidate affiliations since being appointed to the DA’s seat by Republican Gov. Charlie Baker at the beginning of the year. He has also declined to explicitly state whether he intends to continue Rollins’ controversial policy of declining to prosecute 15 non-violent offenses except in special circumstances.

“They are definitely offering two different visions of the DA role,” said political analyst Erin O’Brien, associate professor of political science at the University of Massachusetts Boston. “Hayden can’t out-progressive Arroyo, but it sounds like he can out-experience him, so that’s his best card to play.”

O’Brien acknowledged some segment of Suffolk County voters may cast their votes with the differing stances in mind, but stopped short of calling the race a referendum on Rollins — or progressivism.

“Ideologically, some people will be voting in this race based on their view of the role — how punitive a DA should be, or [how much] restorative justice” a DA should embrace, said O’Brien. “But, I don’t think there’s as much heat on this race because Rachael Rollins was understood as an outsider that didn’t bow to the throne of Massachusetts political insiders ... and it obviously worked out for her.”

Arroyo, who is powered by his own political base and the strength of his family’s political dynasty, is less of an outsider than Rollins was.

In his statement Monday, Arroyo’s campaign also chided Hayden’s for attempting to frame Wu as out of touch with voters.

“We are disappointed that our opponent’s campaign saw fit to question Mayor Wu’s judgment, the first woman and person of color elected as Mayor of Boston,” Missouri said. “We are grateful for Mayor Wu’s endorsement and we know the most important endorsement comes from the voters.”

Wu, too, defended her endorsement against criticism from DA Hayden’s campaign Monday, dismissing the comments as relics of an older era of Boston politics.

“I think many of the comments that we're hearing now are similar to those that we’ve heard for a long time,” the mayor said during an appearance on WBUR’s Radio Boston. “So, the same statements of someone not being old enough or experienced enough, in some ways I think that is code and signal for upholding the status quo. And it’s clear that the residents of Boston — in the mayor’s race, in so many issue-area campaigns and in other races — have said over and over again that it is time to get down to root causes, put out a clear vision and follow through.”

Hayden’s campaign responded to Wu’s comments Monday night by associating the interim DA with progressives and doubling down on the notion that his experience better qualifies him for the job.

“Experience matters. I doubt Mayor Wu would hire a school superintendent with just four years education experience or a police commissioner with just four years of public safety experience,” said Webster in a statement to GBH News.

“The District Attorney is the top public safety position in Suffolk County. The experience this person brings to the job is critically important to keeping residents safe and healthy. Kevin Hayden has over 25 years of public safety and legal experience — as a progressive prosecutor, a defense attorney, and someone who has managed a state agency,” Webster continued. “Ricardo Arroyo has no management experience, no public safety experience, and no prosecutorial experience.”

Massachusetts State Primary elections will take place Tuesday, Sept. 6.