Progressives are taking shots at Joe Biden, seeking to blunt the former vice president's rise in polls by arguing he is too conservative to be the party's presidential nominee.

The criticism has come from rivals to Biden on the campaign trail as well as liberal groups seeking to put a dent into his poll numbers.

They are casting Biden as an establishment figure out of touch with the grass roots of his party, highlighting his work on a Clinton-era crime bill and the Iraq War, among other issues.

The criticism suggests some angst on the part of progressives, who fear Biden might beat out candidates such as Sens. Bernie Sanders (I-Vt.) and Elizabeth Warren (D-Mass.), who have more liberal voting records than the former vice president.

The latest Hill-HarrisX poll released on Monday found Biden winning 46 percent support and holding a 32-point lead nationally over Sanders, who won 14 percent.

Progressives also say they are worried that Biden will lose to Trump, even as the former vice president makes electability the centerpiece of his campaign.

They argue a dyed-in-the-wool progressive has the best chance of energizing voters against Trump, and that Biden could fall to the wayside just as Hillary Clinton did in 2016.

"I think that people's initial, and main concern is that he is out of step with the primary electorate and is going to have the same problems that Clinton did with motivating the base and being the best candidate to run against Trump," said one Democratic strategist. "And then that got turbocharged by him jumping out to an early lead, and all of the [news] articles about people being focused on 'electability' and that again is going to be another Clinton campaign redux."

Sanders is drawing a clear distinction between himself and Biden in interviews.

"I think if you look at Joe's record, and you look at my record, I don't think there's much question about who's more progressive," he said in an interview that aired Sunday on ABC's "This Week."

"Joe voted for the war in Iraq, I led the effort against it. Joe voted for [the North American Free Trade Agreement] and permanent trade relations, trade agreements with China. I led the effort against that. Joe voted for the deregulation of Wall Street, I voted against that," Sanders said.

The comments followed a jab from Warren, who has accused Biden of being too cozy with corporate interests during the Wall Street bailout.

"At a time when the biggest financial institutions in this country were trying to put the squeeze on millions of hardworking families," Warren said last month, "Joe Biden was on the side of the credit card companies."

Progressive groups slammed Biden right as he jumped out of the starting gate.

Justice Democrats described the former vice president as being "in near complete opposition to where the center of energy is in the Democratic Party today."

Advocacy groups and progressive figures have also taken shots at Biden for his praise of various GOP figures. Last week, a 2015 video of Biden that highlighted his relationship with former Vice President Dick Cheney made the rounds on Twitter.

"First of all, I really like Dick Cheney for real," Biden in remarks at the time. "I get on with him. I think he's a decent man."

Bhaskar Sunkara, the author of the new book "The Socialist Manifesto: The Case for Radical Politics in an Era of Extreme Inequality" and the founder of Jacobin Magazine, a quarterly magazine offering socialist perspectives, said it's important to keep the pressure on Biden's candidacy.

He said it's clear Biden has a following among Democrats, and that even though he isn't the most progressive candidate he could win the primary.

"Biden isn't a progressive candidate, but he is a well-liked candidate," Sunkara said.

Sunkara also said that while bringing up Biden's centrist policies could help win supporters for Sanders, Warren or another progressive candidate, it might not be enough. He suggested that progressives need to make Biden's electability a part of the debate, but turn it against him.

"But with the specter of Trump looming, most people just want someone who's electable," Sunkara said. "Portraying Biden as unelectable and gaffe-prone seems to me the most important thing."

In recent weeks, Biden has sought to straddle the line when defining himself. Last month, he called himself an "Obama-Biden Democrat" after a gaggle of reporters in Washington pushed him on whether he was progressive.

He has also said he has "the most progressive record" of any of the 2020 candidates.

Democratic strategist Maria Cardona said she's not sure Biden's centrism will hurt him with Democratic voters, even if the party is moving to the left.

"If you look at the makeup of the Democratic Party, it doesn't seem like it would hurt Biden at all since most Democratic Party voters are still older, more moderate than very liberal and come out to vote in greater numbers than the much younger progressives," she said.

She also said Biden could inoculate himself from such attacks with strong support from African American and Latino voters.