Republican mayoral challenger Paul Massey, at a Queens kosher supermarket Monday to officially launch his campaign, criticized Democratic incumbent Bill de Blasio for “lobbing invective” at President Donald Trump.

But Massey, a multimillionaire real estate executive seeking the mayoralty in the mold of de Blasio’s predecessor Michael Bloomberg, declined to say whether he’d keep or abandon the mayor’s policy of making New York City a so-called “sanctuary city” that aims to shield immigrants from federal deportation. Massey said America needs to develop a national immigration policy while recognizing immigrants’ importance.

Since Trump’s election in November, de Blasio has frequently criticized Trump. Last month the mayor blamed Trump’s rhetoric for an uptick in anti-Semitic crimes.

“The current mayor is lobbing invective at the president right now. I don’t think that’s helpful,” Massey said, standing in front of stack of avocados at Aron’s Kissena Farms supermarket in Queens’ Flushing neighborhood.

Massey said de Blasio was wrong two years ago to boot the federal Immigration and Customs Enforcement agency from Rikers Island, the city’s jail complex, where agents had been stationed to expedite detentions of inmates suspected of being in the United States illegally.

The stop in Queens, where Massey promised to create more jobs as mayor, kicked off what he promised would be a weeklong tour of the five boroughs: an event in the Bronx Tuesday to discuss “homelessness and affordable housing”; another in Brooklyn to talk about education; Thursday in Staten Island for an event on “Quality of life and the opioid epidemic”; and in Manhattan to support “community-focused policing.”

Monday’s event was about jobs, stimulating the economy, and changing the city’s dependency on real estate taxes. Massey also used the event to urge the city’s troubled assessment system to be “fair.” He also discussed his plan to lure jobs from other American cities.

Asked to assess de Blasio’s vow to create 100,000 jobs — many paying $50,000 a year or more — over a decade, Massey said: “I think the mayor has a three-year city record of not doing anything for big business, small business . . . We need to attract major companies. With the biotech industry, we’re getting our lunch eaten by cities like San Francisco, Seattle, Cambridge, Massachusetts. That needs to stop.”

Dan Levitan, de Blasio’s campaign spokesman, ridiculed Massey’s longtime residency in the Larchmont section of Westchester, from which he recently relocated, and also the candidate’s news conference last month where he said he had not “established an answer” about the NYPD’s practice of stop, question and frisk.

“Paul Massey (R-Larchmont) can’t decide how he feels about stop-and-frisk, President Trump, or whether New York should remain a city that protects immigrant families. He is desperate to discuss anything but the issues,” Levitan said in an email. “Mayor de Blasio has created enough affordable housing to shelter the entire population of Paul Massey’s hometown (Larchmont, population: 5,951) more than twenty times over. That’s a record we are happy to compare with anyone.”

Despite probes by federal, state and local anticorruption investigators, de Blasio has maintained commanding leads in opinion polls and fundraising. The mayor fares worst among white voters — many of whom live in the Queens neighborhood Massey visited on Monday.

Massey has highlighted the probes and called de Blasio corrupt. De Blasio maintains that neither he nor his team have done anything wrong. No one has been charged with a crime in the matter.

Barbara Horton, a Democrat who was shopping in the produce section during Massey’s visit, said she’s unsure whom she’ll vote for in November.

“I’m just shopping. My wagon’s still there,” said Horton, a 65-year-old gymnastics teacher from nearby Forest Hills as she pointed to her cart. “I wasn’t shopping for a new candidate.”