New York Democratic Rep. Alexandria Ocasio-Cortez is endorsing the primary challenger running to defeat the head of the House Democratic campaign arm, a rare move from a sitting member of Congress.
Ocasio-Cortez's plans to endorse state Sen. Alessandra Biaggi's bid against Democratic Rep. Sean Patrick Maloney were first reported by the New York Times. Biaggi quickly retweeted the Times' story and included a statement from Ocasio-Cortez.
In a fundraising email to Biaggi and Ocasio-Cortez supporters and obtained by NBC News ahead of its release, the congresswoman will praise Biaggi by saying, "We can count on her to stand with our movement on critical issues such as abortion rights, championing the Green New Deal and Medicare for All, and fighting to raise the minimum wage."
She added that the race will be "competitive and expensive," noting that her "well-funded opponent ... happens to be the chairman of the DCCC."
In a statement responding to the endorsement, Maloney told NBC: "I respect Rep. Ocasio-Cortez and have worked with her on a number of policy matters, including as a co-sponsor of the Green New Deal. But, on her endorsement, we are going to have to agree to disagree."
"This election comes down to voters in NY-17, and I am honored to have received overwhelming support locally, including endorsements from nearly 40 elected leaders and democratic party committees," he said.
Maloney's campaign also provided NBC with a memo from the campaign's pollster showing Maloney leading Biaggi 45 percent to 15 among likely Democratic primary voters with 39 percent undecided. Maloney's favorability rating in the poll is 46 percent, with 13 percent viewing him unfavorably. Fourteen percent of likely Democratic voters viewed Biaggi favorably in the poll, with 10 percent viewing her unfavorably and 76 percent saying they are unfamiliar with her or unable to rate her.
The poll of 385 likely Democratic voters, with a margin of error of 5 percent, was taken between May 26 and June 1.
The endorsement from Ocasio-Cortez comes weeks after redistricting roiled the state's House Democratic caucus, exposing divisions between incumbent members of Congress.
An outside expert had to draw a new congressional map after a state judge overruled the legislature's proposed plan. That new map sparked a scramble that led to a handful of Democratic members running against each other.
Maloney avoided that fate when his home was drawn into the district that included much of progressive Democratic Rep. Mondaire Jones' current seat. Jones decided to run in a different district instead of facing off against Maloney, a powerful member of party leadership.
Maloney's decision to run in the new district — a more friendly one for Democrats compared to what was left of his old district — prompted some criticism from progressives. Ocasio-Cortez called on Maloney to resign his post leading the Democratic Congressional Campaign Committee, telling Politico the decision "further imperils our majority.” Maloney has defended the decision by noting that the new map put him in that new district.
Ocasio-Cortez has endorsed some challengers to Democratic incumbents in the past and she's no stranger to taking on her party's leadership. She defeated a top Democrat herself, besting former Caucus Chairman Joe Crowley in a primary in 2018.
-- This story was updated on June 7, 2002 at 2:45 p.m. ET.