Rep. Alexandria Ocasio-Cortez will endorse Sen. Bernie Sanders for president, The Washington Post reported Tuesday night, a political coup for the Vermont senator as he looks to increase his standing in the polls for the 2020 Democratic presidential nomination.

"This is big," said Politico campaign reporter Holly Otterbein after confirming the news with members of the Sanders campaign.

According to the Post:

The endorsement could be a blow for Sen. Elizabeth Warren (D-Mass.), who, like Sanders, is running on a platform of sweeping liberal change and who has emphasized her role as a female pioneer. Ocasio-Cortez had worked as a volunteer organizer for Sanders’s 2016 presidential bid; she was recruited to run for Congress in 2018 by Justice Democrats, a group that grew out of the Sanders campaign. [...] Her backing was a sought-after prize in the Democratic primary, and it was widely assumed that she would endorse either Sanders or Warren, the most liberal figures in the contest.

"This was always to be expected," The Intercept's Medhi Hasan said on Twitter. "He's the candidate most in line with her values and policies—even more so than Warren."

Reps. Ilhan Omar (D-Minn.) and Rashida Tlaib (D-Mich.) will also endorse Sanders, reported CNN's Greg Krieg.

"Bernie is leading a working class movement to defeat Donald Trump that transcends generation, ethnicity and geography," Omar said in a statement, adding, "it's why I believe Bernie Sanders is the best candidate to take on Donald Trump in 2020."

"Ilhan is a leader of strength and courage," said Sanders. "She will not back down from a fight with billionaires and the world’s most powerful corporations to transform our country so it works for all of us. I'm proud of what we've done in Congress, and together we will build a multiracial working class coalition to win the White House."

New: Ilhan Omar and Rashida Tlaib will also endorse Sanders, according to source. AOC will, as @daveweigel and @WaPoSean first reported, will do the same on Saturday in NYC. — Greg Krieg (@GregJKrieg) October 16, 2019

Ocasio-Cortez, Tlaib, and Omar—representing three of the four progressive House freshman known as "the Squad"—are expected to appear alongside Sanders at a rally in New York City Saturday.

"We're looking forward to Saturday," Ocasio-Cortez spokesman Corbin Trent told the Post.

The news broke in the waning minutes of a primary debate featuring Sanders and 11 of his rivals for the nomination in which Sanders and Sen. Elizabeth Warren (D-Mass.) fended off attacks from more right wing candidates on issues like Medicare for All, Sanders' signature legislation.

"Between his stellar performance at the debate tonight and AOC's pending endorsement," tweeted Al Jazeera journalist Sana Saeed, "this is a huge moment and Sanders cannot, and should not, be ignored any longer by those who continue to erase him, his candidacy, and his supporters."

Reflecting on the strong performance and the endorsement, Young Turks reporter Emma Vigeland called it "a historic night for the Sanders campaign."

"These endorsements just fired me up even more," said activist Linda Sarsour.