Alexandria Ocasio-Cortez is prepared to issue her first endorsement of a liberal challenger to a Democratic incumbent, in a move that could test her sway in a party that has remained largely resistant to her brand of progressive politics.

Ms Ocasio-Cortez, a congresswoman from New York City who surprised the nation by beating an entrenched Democrat in her Queens district during the 2018 primary, will reportedly endorse Illinois candidate Marie Newman.

Ms Newman is seeking to unseat Daniel Lipinski, a conservative-leaning Illinois Democrat who represents a district southwest of Chicago.

The Illinois challenger is a businesswoman, and has already garnered support from the group Justice Democrats, which backed Ms Ocasio-Cortez in her primary bid two years ago against a long-term Democrat in the Bronx and Queens who she said then was out of step with his constituents.

Ms Newman, who calls herself a “real Democrat”, has also run against Mr Lipinski previously, in 2018 when she lost by 2,000 votes.

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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,” Ms Ocasio-Cortez told the New York Times.

Ms Ocasio-Cortez then went after Mr Lipinski, noting the congressman — who votes in line with Donald Trump’s policies nearly one-third of the time, according to an analysis by FiveThirtyEight — serves in a safe Democratic district, but frequently sides with conservatives.

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“The fact that a deep blue seat is advocating for many parts of the Republican agenda is extremely problematic,” Ms Ocasio-Cortez said. “We’re not talking about a swing state that is being forced to take tough votes.”