Former U.S. Vice President Joe Biden delivers remarks during the National Minority Quality Forum on April 9, 2019 in Washington, DC.

Sens. Elizabeth Warren, D-Mass., and Bernie Sanders, I-Vt., both appeared to take shots at former Vice President Joe Biden in his first official day on the campaign trail.

Their remarks offered some of the first intraparty criticism to emerge from the pool of at least 20 Democrats running to defeat President Donald Trump in the 2020 election. When Biden joined the race Thursday, he was widely viewed as an instant front-runner.

On Thursday, Sanders' campaign sent a shot across the bow at Biden in response to a reported fundraiser in Philadelphia on Thursday evening at the home of Comcast Senior Executive Vice President David Cohen. Comcast owns CNBC parent NBCUniversal.

In an email to supporters sent Thursday under the subject line "Joe Biden," the self-described democratic socialist's campaign wrote: "It's a big day in the Democratic primary and we're hoping to end it strong. Not with a fundraiser in the home of a corporate lobbyist, but with an overwhelming number of individual donations."

Warren, meanwhile, dredged up her past criticisms of Biden's record on financial issues during his three decades in the Senate.

"Joe Biden was on the side of credit card companies," Warren said Thursday at an event in Iowa when asked about Biden's relationship to Wall Street, according to The New York Times.

Her disagreement with Biden over bankruptcy legislation "is a matter of public record," she said.

Kaplan TWEET WARREN, asked by a reporter about Biden and Wall Street, says their disagreement over bankruptcy legislation "is a matter of public record." She puts it bluntly: "Joe Biden was on the side of credit card companies."

Indeed, Warren targeted Biden in her 2014 autobiography for his sponsorship of a bill supported by the financial services industry that tightened rules on consumers seeking bankruptcy protections.

"The Senate was evenly split between the two parties, but one of the bill's lead sponsors was Democratic powerhouse Joe Biden, and right behind him were plenty of other Democrats offering to help," Warren wrote, the Times reported. "Never mind that the country was sunk in an ugly recession and millions of families were struggling — the banking industry pressed forward and Congress obliged."