Left-wing Democrats have exulted after democratic socialists emerged victorious from House primaries in deep-blue New York districts this week.

But centrist Democrats have reacted with a very different tone. Alarm.

“We are capitalist, not socialist,” reads a letter, titled “The Promise to America,” signed by a group of moderate House Democrats two days after the primaries.

With four months until the midterm elections, the outcomes in New York have deepened divisions in the Democratic Party, threatening to unleash a renewed internal debate about electability and how Democrats speak about capitalism. In Congress and elsewhere, some moderates have quickly distanced themselves from the victorious far-left candidates, worrying Republicans will use them to paint the entire party as extreme.

Organizers of the letter, which had been released earlier this month, unveiled the first 15 signatories on Thursday — two days after primary results that put democratic socialists on track to double their ranks in the House.

“Politics forces false choices between extremes on right and left,” the letter said. “We reject them.”

The letter is led by Representative Tom Suozzi, a New York Democrat who flipped a swing district on Long Island two years ago. He said the group aimed to secure signatures from 20 Democratic candidates, 200 state and local officials, and 2,000 activists — and to “build a movement.”