During this week’s Democratic Party’s debate in Los Angeles, Mr Buttigieg clashed with progressive senator Elizabeth Warren, over the event he held at the Hall Rutherford Winery in Napa Valley.

“We made the decision many years ago that rich people in smoke-filled rooms would not pick the next president of the United States,” she said.

“Billionaires in wine caves should not pick the next president of the United States.”

Mr Buttileg was quick to fire back, pointing to a Forbes magazine article that said he was the only individual among the seven on stage who was not a “millionaire or a billionaire”.

Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures Show all 15 1 /15 Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures Alexandria Ocasio-Cortez greets fellow lawmakers ahead of the State of the Union address Getty Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures Alexandria Ocasio-Cortez participates in an event with Democratic members of Congress EPA Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures The Democrat senator speaks during a news conference at the U.S. Capitol January 30, 2019 Getty Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures Alexandria Ocasio-Cortez and fellow Democrat Rashida Tlaib AP Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures Alexandria Ocasio-Cortez at the Senate chamber to watch two votes on January 24, 2019 Getty Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures Alexandria Ocasio-Cortez arrives with Chellie Pingree at a House Democratic Caucus meeting Getty Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures Ocasio-Cortez during Donald Trump's State of the Union address Reuters Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures New York State Assembly member Catalina Cruz with Ocasio-Cortez AFP/Getty Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures Nydia Velazquez talks with Alexandria Ocasio-Cortez Reuters Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures Ocasio-Cortez casts her vote for Nancy Pelosi as Speaker of the House EPA Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures Alexandria Ocasio-Cortez poses with a campaign worker during a whistle stop in the Queens borough of New York Reuters Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures Ocasio-Cortez outside the US Capitol AFP/Getty Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures Ocasio-Cortez after casting her ballot in the 2018 midterm general election at a polling site in New York EPA Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures Alexandria Ocasio-Cortez looks on during a march organised by the Women's March Alliance in Manhattan Reuters Alexandria Ocasio-Cortez - the Democratic congresswoman in pictures Ocasio Cortez looks on at the Capitol in Washington, DC, on January 16, 2019 AFP/Getty

“So, this is important. This is the problem with issuing purity tests you cannot yourself pass,” he said.

On Saturday, attending a rally with fellow progressive Bernie Sanders, Ms Ocasio-Cortez attacked the mayor of South Bend without naming him.

“This is the revolution,” she said, speaking at Venice Beach. “And by the way, anyone who accuses us of instituting purity tests, it’s called having values, it’s called giving a damn.”

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Ms Ocasio-Cortez, who once worked as a waitress, added: “Let me tell you something I go to work all the time and I hear people say, “what will my donors think”? I hear that phrase. And I hear and I see that billionaires get members of Congress on speed dial and waitresses don’t.”

Mr Sanders, who has been endorsed for the presidency by Ms Ocasio-Cortez, the youngest ever member of Congress, also referred to Mr Buttigieg’s fundraising.

“We don’t go to rich people’s wine caves,” he said, according to the Daily Mail.

Meanwhile, the owners of the winery where the event was held, Craig and Kathryn Hall, took issue with how their wine cave has been portrayed in the media.

“It seems someone’s intentionally trying to create a different image than the reality. And that’s unfortunate,” Mr Hall told the Associated Press.

“I don’t think anyone came with the expectation that they were going to become Pete’s good buddy for some personal purpose.”