Former South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBipartisan praise pours in after Ginsburg's death Bogeymen of the far left deserve a place in any Biden administration Overnight Defense: Woodward book causes new firestorm | Book says Trump lashed out at generals, told Woodward about secret weapons system | US withdrawing thousands of troops from Iraq MORE took an apparent dig at Sen. Bernie Sanders Bernie SandersKenosha will be a good bellwether in 2020 Biden's fiscal program: What is the likely market impact? McConnell accuses Democrats of sowing division by 'downplaying progress' on election security MORE (I-Vt.) in a fundraising email, implying his 2020 rival is a Washington insider.

The email also appeared to take a dig at his fellow billionaire rivals Michael Bloomberg Michael BloombergTop Democratic super PAC launches Florida ad blitz after Bloomberg donation The Hill's 12:30 Report - Presented by Facebook - Latest with the COVID-19 relief bill negotiations The Memo: 2020 is all about winning Florida MORE and Tom Steyer Tom SteyerTV ads favored Biden 2-1 in past month Inslee calls Biden climate plan 'perfect for the moment' OVERNIGHT ENERGY: Trump administration finalizes plan to open up Alaska wildlife refuge to drilling | California finalizes fuel efficiency deal with five automakers, undercutting Trump | Democrats use vulnerable GOP senators to get rare win on environment MORE as "people who can spend millions of their own dollars on a campaign," though Buttigieg did not name them.

"Some of our competitors, like Bernie Sanders, have even run for president before -- and that means that they had a head start on things like building their fundraising lists," the email reads. "Having several million people on your email list allows you to do things like raise $4 million in two days -- something Bernie says he did in the 48 hours after the last debate."

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"If we are going to turn the page on our politics, we have to be able to compete with the people who have been working in Washington for years, and the people who can spend millions of their own dollars on a campaign. That means we need your help right now with another donation to this campaign," it continues.

Buttigieg has previously aimed his fire on Sanders's progressive counterpart, Sen. Elizabeth Warren Elizabeth WarrenBiden's fiscal program: What is the likely market impact? Warren, Schumer introduce plan for next president to cancel ,000 in student debt The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon MORE (D-Mass.), clashing with her in the two previous primary debates.

The 37-year-old former mayor has run as an outsider to Washington, D.C., and has advocated a more moderate platform than Sanders or Warren.

Although Sanders was first elected to Congress in 1990, he has often been viewed as a Washington outsider for the majority of his career, supporting a number of progressive issues like "Medicare for All."

Sanders most recently went against the mold on Thursday, when he joined nine other senators in voting against the U.S.-Mexico-Canada Agreement.

The Vermont senator has also pushed back against the Democratic Party establishment and took the political world by surprise in 2016 in his unexpectedly strong challenge to Democratic-establishment favorite, Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE.

The Hill has reached out to the Sanders campaign for comment.