Rep. Dan Lipinski (D-IL) defended his Chicago-area seat against Rep. Alexandria Ocasio-Cortez (D-NY), who is backing primary challenger Marie Newman, a “progressive” candidate whom he defeated in the 2018 primary.

Ocasio-Cortez backed Newman in a tweet on Tuesday:

Marie Newman (@Marie4Congress) is a grassroots fighter for working families in #IL03. To me, choosing to support is about more than just policy. It’s also about who puts in the WORK. Are they wearing out their shoes? Marie is. Her supporters are. Let’s knock doors & join them. https://t.co/jjSy4Anc14 — Alexandria Ocasio-Cortez (@AOC) September 17, 2019

It was Ocasio-Cortez’s first endorsement of a primary challenger to an incumbent Democrat in the 2020 cycle.

Lipinski, one of the few remaining pro-life Democrats, defeated the pro-choice Newman in a heated primary contest last year. Lipinski also voted against Obamacare in 2010. Newman also holds a number of other left-wing opinions.

In a statement, Lipinski said that Ocasio-Cortez’s endorsement proved Newman is too “extreme” for the 3rd congressional district, and said voters “do not want to be represented by a fifth member of the ‘Squad’.”

Dan Lipinski responds to @AOC endorsing his primary opponent and it’s a doozy. “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.'” pic.twitter.com/zewNDe6CfP — Alex Seitz-Wald (@aseitzwald) September 17, 2019

The “Squad” is a nickname Speaker Nancy Pelosi (D-CA) bestowed upon Ocasio-Cortez and Reps. Ilhan Omar (D-MN), Rashida Tlaib (D-MI), and Ayanna Pressley (D-MA), who tend to vote together and take far-left positions.

Lipinski also criticized Newman for supporting the “Medicare for All” plan that left-wing Democrats have backed, arguing that it would take private health insurance away from 170 million people and double federal income taxes for the average family in his working-class district.

Ocasio-Cortez responded by calling Lipinski’s statement “divisive.”

Joel B. Pollak is Senior Editor-at-Large at Breitbart News. He earned an A.B. in Social Studies and Environmental Science and Public Policy from Harvard College, and a J.D. from Harvard Law School. He is a winner of the 2018 Robert Novak Journalism Alumni Fellowship. He is also the co-author of How Trump Won: The Inside Story of a Revolution, which is available from Regnery. Follow him on Twitter at @joelpollak.