NEW YORK (CBSNewYork) — Police Commissioner Bill Bratton is fighting back after New Jersey Gov. Chris Christie claimed Mayor Bill de Blasio’s policies have increased crime in New York City.

During an appearance on MSNBC’s “Morning Joe” on Tuesday, de Blasio touted statistics showing the city is enjoying its safest summer in two decades.

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“I think the facts count for a lot,” de Blasio said. “I think if you talk to everyday New Yorkers about their quality of life, what they’re experiencing, people know it was the safest summer in 20 years because they’re experiencing it.”

Moments later, the Republican presidential candidate appeared on the network, disagreeing with de Blasio.

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“It’s less safe in this city,” Christie said, adding that de Blasio’s “liberal policies” are diminishing the quality of life in the city. “For those families that lost their loved one, I don’t think they thought it was a safer summer.”

Bratton fired back Thursday morning, telling CNN, “As far as Gov. Christie, he doesn’t know what the hell he’s talking about. … Crime is not up overall in New York City, it’s down by 3.9 percent.”

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There is a slight uptick in murders, but Bratton said that’s compared to 2014, which saw the lowest number of killings in recent history.