WASHINGTON — The House Democratic campaign arm is nearing open warfare with the party’s rising liberal wing as political operatives close to Speaker Nancy Pelosi try to shut down primary challenges before what is likely to be a hard-fought campaign next year to preserve the party’s shaky majority.

Progressive Democrats were infuriated last month when Representative Cheri Bustos of Illinois, the chairwoman of the campaign arm, the Democratic Congressional Campaign Committee, moved to protect centrist incumbents by formally breaking committee business ties with political consultants and pollsters who go to work for primary challengers.

Representative Alexandria Ocasio-Cortez, Democrat of New York, who owes her seat to a successful primary challenge, went so far as to encourage her 3.8 million Twitter followers to “pause” their donations to the campaign committee in protest. She also started a fund-raising push on her official Twitter account for Representatives Jahana Hayes of Connecticut, Katie Hill of California and Mike Levin of California. That initiative, Ms. Ocasio-Cortez said on Twitter, raised $30,000 in roughly two hours. She also helped raise money for Representatives Katie Porter of California and Lauren Underwood of Illinois.

The open hostilities are just the latest in the rising tensions between an experienced party establishment focusing on what is possible in the short run and a group of young liberals chafing at such restraint. House Democrats have divided over single-payer “Medicare for all” versus incremental legislation to bolster the Affordable Care Act and over Ms. Ocasio-Cortez’s Green New Deal versus less ambitious climate change policies. Liberal Democrats and more moderate newcomers from Republican-leaning districts have fought over Republican procedural motions.