Amid deteriorating relations with his fellow Democrats, Philadelphia District Attorney Seth Williams has hired Republicans to manage his reconstituted fund-raising operation, the Inquirer reported Monday. Williams, whose past political spending has drawn federal scrutiny, explained that his new team of onetime rivals is "working to professionalize" his campaign finances so he can "focus . . . on doing the important work in the District Attorney's Office."

The heartening implication is that Williams' campaign finances are separate from his law enforcement. But the district attorney has indicated just the opposite, and set a disturbing precedent, by bowing out of what could be his office's highest-profile case due to the involvement of a supporter.

In declining to investigate a construction site brawl in which the combatants included one of the city's most powerful Democrats, electricians' union leader John J. Dougherty, Williams has cited his "long-standing professional relationship" with the labor boss. Dougherty's International Brotherhood of Electrical Workers Local 98 has given a total of $17,500 to Williams' campaign committee since opposing his first successful run for the office.

Williams' recusal has had the unfortunate result of outsourcing the investigation to the office of state Attorney General Kathleen Kane, who is not only facing criminal charges and impeachment proceedings but has also received more money from the electricians than Williams has. In fact, a Kane spokesman said the attorney general would recuse herself from the case too, though, unlike Williams, she has directed her subordinates to look into the punch-up.

The FBI is also reportedly on the case, which is reassuring in light of the reluctance of local law enforcers. On the other hand, street fights do not normally constitute federal crimes; that's why we have a district attorney.

The Inquirer reported on Sunday that the January brawl was the second in as many years pitting Dougherty and other union members against nonunion workers at a South Philadelphia construction site. Remarkably, a police spokeswoman said the earlier fight, dating to May 2014, is still under investigation. One hopes it won't take two years to sort out conflicting accounts of the latest melee, but the official response so far isn't encouraging.

Williams may have been forced to turn to Republican campaign professionals for at least one good reason: his willingness to prosecute a gaggle of corrupt Democrats whom the attorney general was prepared to let walk. While that seems to have upset his fellow partisans, it showed one of Williams' strengths as a prosecutor. Indeed, Williams has sharply and rightly criticized his predecessor, Lynne Abraham, for avoiding politically sensitive cases. He won't improve his political prospects, or the credibility of the city's justice system, by abandoning that stance and abdicating his duty to enforce the law without fear or favor.