Rep. Alexandria Ocasio-Cortez talks to reporters outside the US Capitol building.

Rep. Alexandria Ocasio-Cortez's surprise endorsement of Sen. Bernie Sanders' 2020 presidential bid is a big win for Sanders and could potentially hurt Sen. Elizabeth Warren, his rival for the progressive vote.

Despite an ideological cleavage in the Democratic Party, Ocasio-Cortez is very popular among self-identified Democratic primary voters across the board, according to recent Insider polling.

But the 30-year-old Bronx native is most popular among voters who support Warren, which makes her endorsement move particularly unfortunate for the Massachusetts lawmaker.

About 55% of Sanders' supporters, and 63% of Warren supporters, have a favorable opinion of Ocasio-Cortez, according to recent Insider polling.

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Rep. Alexandria Ocasio-Cortez's recent surprise endorsement of Sen. Bernie Sanders' 2020 presidential bid is a big win for Sanders and could potentially hurt Sen. Elizabeth Warren, his rival for the progressive vote.

Despite an ideological cleavage between the left and centrist wings of the Democratic Party, Ocasio-Cortez is very popular among self-identified Democratic primary voters across the board, according to recent Insider polling conducted October 15-16 among 1,095 respondents, 448 of whom said they'd likely participate in the Democratic primary.

About 45% of those Democratic voters have a "strongly favorable" or "favorable" opinion of the freshman congresswoman, while about 12% have either a strongly unfavorable or unfavorable opinion. About a quarter — 26% — have neither a favorable nor unfavorable opinion, and 17% don't know who she is.

Read more: How the INSIDER 2020 Democratic primary tracker works

Ocasio-Cortez's favorability shoots up among Sanders' supporters, 55% of whom have a favorable view of the lawmaker.

But the 30-year-old Bronx native is most popular among voters who support Warren — 63% have a favorable opinion of AOC, which makes her endorsement of Sanders particularly harmful to the Massachusetts lawmaker.

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Based on polling we conducted in July, the AOC endorsement is the single-most coveted endorsement of any Democrat who has not been a president before. A quarter of Democrats then said that they'd value Ocasio-Cortez's endorsement in the primary, putting her higher than 2016 presidential nominee and fellow New Yorker Hillary Clinton and just shy of the 27% who value the endorsement of former President Jimmy Carter.

Read more: Alexandria Ocasio-Cortez's endorsement of Bernie Sanders is a huge win for him and a way for her to hit back at the Democratic Party

Notably, Ocasio-Cortez's favorability is at 45% among former Vice President Joe Biden's supporters, despite her repeated attacks on Biden's positions on a range of issues, including climate change.

Given Ocasio-Cortez's broad popularity among primary voters and even Biden supporters, the former vice president could suffer in the primary if he attempts to distance himself further from Ocasio-Cortez and her allies on the left.

SurveyMonkey Audience polls from a national sample balanced by census data of age and gender. Respondents are incentivized to complete surveys through charitable contributions. Generally speaking, digital polling tends to skew toward people with access to the internet. SurveyMonkey Audience doesn't try to weight its sample based on race or income. Total 1,095 respondents collected October 15-16, 2019, a margin of error plus or minus 3.04 percentage points with a 95% confidence level. There were 448 respondents who said they'd participate in the Democratic primary.

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