A day after becoming the Democratic candidate for district attorney, Larry Krasner responded to a swell of criticism from the local police union, the Republican Party, and prosecutors about the prospect of the long-time civil rights attorney's serving as Philadelphia's top law enforcement officer.

Krasner, 56, a criminal defense attorney for 30 years, finished first in a field of seven Tuesday with a progressive agenda that promised criminal justice reform, a moratorium on seeking the death penalty, and a crackdown on police misconduct. In Philadelphia, where Democrats outnumber Republicans by 7-1, Krasner in November will face Republican Beth Grossman.

But concerns among some members of law enforcement over what the office would become with an outsider at the helm were fanned Tuesday night when a small group of Krasner supporters at his election-night party began a profanity-laced chant aimed at the Fraternal Order of Police,  the police union.

John McNesby, president of FOP Lodge 5,  called the Krasner supporters who chanted against police "the parasites of the city" on Wednesday and again lambasted Krasner's candidacy.

"His election to that position would be catastrophic to the department and the community as a whole," McNesby said.

Krasner defended his supporters' First Amendment rights to chant, "No good cops in a racist system," as well as a more pointed refrain aimed at the FOP.

"I'm a great believer in free speech," Krasner said at a news conference in Center City on Wednesday afternoon. "That does not mean I always agree with everything that is said."

Krasner said he was confident he could work well with police and prosecutors in the District Attorney's Office. He dismissed the criticism as politics fueled by the Republican Party and unions, not rank-and-file police. The city's Republican Party sent out a fund-raising email Wednesday citing the chant and seeking donations to defeat Krasner, whom it dubbed an "anti-law-enforcement radical."

"These are unions. They are not the commissioner. They are not the brass," Krasner said. "They're not even police in the sense of being on active duty."

Six officers who spoke Wednesday on condition of anonymity reported a common fear that Krasner – who has sued law enforcement more than 75 times – would seek to make an example of any officer involved in a shooting or other altercation, even if the officer's action was justified. They said morale in the department was low after his primary victory.

"It puts you on edge," said Officer Eddie Lopez Sr., president of the city's Spanish American Law Enforcement Association. "Now you're going to have to second-guess yourself, which is not a good thing. It could end up costing your life or a civilian's life if you second-guess yourself."

McNesby, calling Krasner "anti-law enforcement," went so far as to suggest police wait to act when confronted by a dangerous situation while on duty.

"Pull over to the side of the road and call the District Attorney's Office," he said. "Don't do a damn thing, because you're not going to be covered."

Krasner dismissed McNesby's suggestion that should he be elected, police might lie down on the job out of fear of prosecutorial retaliation.

"It's irresponsible to suggest that law enforcement officers, who are paid by taxpayers, would not do what they are required and ordered to do by the police commissioner but would still be taking home a paycheck," Krasner said. "That would be advocating a crime."

Krasner said he had a constructive conversation with Police Commissioner Richard Ross by phone Wednesday afternoon.

"I'm extremely optimistic that if elected, I will work very, very closely and very well with the  progressive commissioner, who's trying to modernize the Police Department and has frankly needed the backing of a progressive DA for a very long time," he said.

The FOP has not determined whom it will endorse in the general election, McNesby said. He put out an invitation to both candidates to meet with the union.

"I can tell you we're going to be talking to Beth and anybody else that may come out as an independent in the future," he said. "Listen, we're not going to shut our doors on this guy [Krasner] either. If he wants to talk, we'll be available."

Grossman, reached Wednesday, said she thinks some of the early discontent from law enforcement could bode well for her campaign come November.

"Throughout the entire primary, [Krasner's] done nothing but express contempt for prosecutors, for the office, for all those candidates who've had prosecutorial experience," Grossman said. "This cannot be a social experiment. This is about keeping our city safe."

Staff writer Chris Palmer contributed to this article.