Former Vice President Joe Biden Joe BidenPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Hillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Fox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio MORE hammered Sen. Elizabeth Warren Elizabeth WarrenHillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns On The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline Democratic senators ask inspector general to investigate IRS use of location tracking service MORE (D-Mass.) Saturday as the conflict between the two 2020 frontrunners continues to escalate. Biden defended his record as an unwavering Democrat who has been loyal to the party for many years after Warren criticized her opponent for his health care plan.

“Yesterday, Elizabeth Warren suggested I was ‘running in the wrong presidential primary’ because I believe in building on Obamacare — not getting rid of it. That's so wrong, it’s almost laughable. I’ve been a card-carrying Democrat since I was 27. And I am running for president because of my progressive record,” Biden wrote in an email to supporters, hitting Warren for registering as a Republican for years before becoming a Democrat.

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“If my opponents want to have a debate on what they've done to truly implement progressive, meaningful change in our country — not what they’re planning, not what they’re proposing, but what they’ve accomplished — I welcome it,” he added, swiping at Warren’s “I’ve got a plan for that” mantra. “But to hurl insults because we don’t share the same approach for the best way to get to the same goal…well that is something I would expect in the other primary.”

The email is the latest salvo in a burgeoning feud between the two Democrats as they battle for the helm of the crowded 2020 primary field.

Biden slammed Warren’s “Medicare for All” plan Friday, saying that the plan's proposed $9 trillion tax on employers would be passed off to companies’ employees.

“For months, Elizabeth Warren has refused to say if her health care plan would raise taxes on the middle class, and now we know why: because it does,” said Biden deputy campaign manager Kate Bedingfield. “Senator Warren would place a new tax of nearly $9 trillion that will fall on American workers.”

Warren shot back that Biden was running in the wrong primary.

“Democrats are not going to win by repeating Republican talking points and by dusting off the points of view of the giant insurance companies and the giant drug companies who don’t want to see any change in the law that will bite into their profits,” Warren fired back.

“But if anyone wants to defend keeping those high profits for insurance companies and those high profits for drug companies and not making the top 1 percent pay a fair share in taxes and not making corporations pay a fair share in taxes, then I think they’re running in the wrong presidential primary," she added.

Warren and Biden have swapped leads in national and early state polls with the Iowa caucuses less than 100 days away.

The feud underlines a broader schism within the Democratic Party between centrists and progressives. Biden, who hast sought to appeal to moderates, has slammed liberal policies as pie-in-the-sky ideas that would skyrocket taxes, while Warren, a longtime progressive, has argued that bold ideas are needed to shake up historical inequities in government policies.