New York Congresswoman Alexandria Ocasio-Cortez has made her first endorsement of a primary candidate who is challenging a sitting Democratic member of the House, announcing Tuesday that she'll support Marie Newman in her effort to defeat Illinois Congressman Dan Lipinski.

Newman nearly defeated Lipinski in the 2018 Democratic primary. Lipinski is one of the most conservative members of the Democratic caucus and is known for his anti-abortion rights positions and his vote against the Affordable Care Act.

"It's going to take a bigger, stronger Democratic Party — one that's returned to our FDR roots & fights for working people — to change our future in 2020. We can't afford deep blue seats fighting against healthcare & equal rights. We need @Marie4Congress," Ocasio-Cortez wrote on Twitter, tagging Newman's Twitter account.

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"Marie Newman is a textbook example of one of the ways that we could be better as a party — to come from a deep blue seat and to be championing all the issues we need to be championing," Ocasio-Cortez said in an interview with the New York Times. "The fact that a deep blue seat is advocating for many parts of the Republican agenda is extremely problematic. We're not talking about a swing state that is being forced to take tough votes."

In a statement, Lipinski hit back against Ocasio-Cortez, who is a member of a cadre of progressive congresswomen known colloquially as the "Squad." Ocasio-Cortez and fellow Squad members — Congresswomen Ilhan Omar, Ayanna Pressley and Rashida Tlaib — have been popular targets for Republicans and President Trump, thanks to their support for policies such as Medicare for All and the Green New Deal.

Lipinski said that Ocasio-Cortez's endorsement "makes crystal clear that Ms. Newman is an extreme candidate who is completely out of step with the voters of Illinois' Third District who do not want to be represented by a fifth member of the 'Squad.'"

In a tweet responding to Lipinski's statement, Ocasio-Cortez said that his words were "aggressive."

"Aggressive statements like these are so casually thrown from corporate candidates towards grassroots ones, yet they never get branded as "divisive," despite their rhetoric. We should ask ourselves why that is," Ocasio-Cortez wrote.

Newman has also been endorsed by Justice Democrats, the progressive group which supported Ocasio-Cortez in her successful 2018 primary campaign against Congressman Joe Crowley. Justice Democrats have also endorsed another primary candidate challenging incumbents in 2020, Jessica Cisneros, who is running against Texas Congressman Henry Cuellar. It is unclear whether Ocasio-Cortez will endorse Cisneros, who also has the support of Senator Elizabeth Warren.