Bernie Sanders Bernie SandersThe Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power Bernie Sanders: 'This is an election between Donald Trump and democracy' The Hill's 12:30 Report: Trump stokes fears over November election outcome MORE's presidential campaign on Monday sought to dismiss arguments that their candidate is yesterday's news, issuing a memo that said the Vermont senator is better positioned than any other candidate to defeat President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE.



Sanders’s campaign manager Faiz Shakir pointed to a spate of public polls since March that show Sanders beating Trump in hypothetical match-ups.

What’s more, he wrote, “the surveys show Sanders with the strongest base of support among voters who say they have committed to one candidate.”





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“We have a lot of work in front of us in the next eight months — but we are more confident than ever that our strong grassroots campaign will lead us to victory in Iowa, New Hampshire, South Carolina and the other early voting states,” Shakir wrote.Sanders, who beat expectations in 2016 to become a household political name and nearly defeatfor the Democratic nomination, is facing a very different race this time.

Instead of a one-on-one race with a mainstream behemoth like Clinton, Sanders is facing one big centrist candidate in 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, and is battling a number of other political stars for attention in the Democratic race.

Sanders has been lodged in second place behind Biden in most polls, but has several other candidates nipping at his heels. The most notable is 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.), a fellow progressive who has been the field’s leader in pitching policy proposals.



Warren has appeared to surge in polls in recent weeks, raising questions about whether she could surpass Sanders — and whether the two liberals were in each other's way.

A recent survey of likely Democratic caucusgoers in Iowa conducted for the Des Moines Register and CNN showed Sanders and Warren in a statistical tie, at 16 percent and 15 percent respectively. Biden, meanwhile, came in at 24 percent support, putting him comfortably in first place.



And a Monmouth University poll of Democratic voters in Nevada released last week showed Warren pulling into second place, behind Biden, with 11 percent support. Sanders came in third with 9 percent.



Shakir acknowledged in his memo on Monday that “other competitors have improved their position in the Democratic primary,” a possible reference to Warren. But, he added, “Sanders has maintained his second-place position in every national poll, and many state polls.”



The memo also underscores the extent to which Sanders has relied on his core base of supporters to power his presidential bid.

In it, Shakir cites two recent polls — one by CBS and the other by The Economist and YouGov — showing that the Vermont senator’s supporters are the most likely to say that they are considering only one candidate for the Democratic nomination.

The argument from the Sanders campaign can be read as a message to rivals that the senator’s core supporters aren’t going anywhere, and that others should join his train.

But one Democratic operative, who spoke on the condition of anonymity to talk candidly about Sanders’s campaign, said that Sanders has done little to broaden his support beyond his base of progressives and young people.

At the same time, Biden’s entrance into the race and Warren’s recent rise have highlighted flaws behind a Sanders base-first strategy, the person said.



“He’s getting pinched on several sides,” the operative said. “One, by Biden’s entrance into the race; when Biden wasn’t in the race, he was polling a bit better. And two, Warren has clearly gotten her groove going.”



For the moment, at least, Warren holds the distinction of being the most direct challenger to Sanders. The two are the most ideologically similar of any two candidates in the Democratic primary field, and are gunning for the support of many of the same voters.



But unlike Sanders, a self-described democratic socialist who has called for a sweeping political revolution, Warren has hinged her strategy on a steady series of policy rollouts, while embracing what she has called “capitalism with serious rules.”



Sanders, meanwhile, has leaned into the socialist moniker. Just last week, he delivered a lengthy speech in Washington defending democratic socialism.



Shakir said in an interview last week that the speech had nothing to do with Sanders’s recent polling numbers, adding that the campaign had been discussing it for months. Rather, Shakir said, the address was a chance for Sanders to define his ideology in the face of Republican attacks.



“Part of what you saw there was an effort to say ‘If I’m the Democratic nominee, I’m going to be ready to answer the charge,’ ” Shakir said.

Part of the challenge for both Sanders and Warren is convincing voters they will be able to take on Trump and win, said Chris Kofinis, a Democratic pollster whose firm Park Street Strategies released a poll on Monday showing Biden as the favorite to defeat the president in 2020.



To be sure, Biden isn’t the only candidate seen as capable of beating Trump. Sixty-nine percent of respondents in the Park Street poll said that Sanders could "definitely" or "probably" beat Trump, while 62 percent said that Warren and Sen. Kamala Harris Kamala HarrisHundreds of lawyers from nation's oldest African American sorority join effort to fight voter suppression Biden picks up endorsement from progressive climate group 350 Action 3 reasons why Biden is misreading the politics of court packing MORE (D-Calif.) could, as well.



But unlike Sanders and Warren, who have put calls for expansive political and economic change front and center in their campaigns, Biden has made the case that defeating Trump should be Democrats’ No. 1 priority – and that he is best equipped to do that.



And in an election cycle in which Democratic primary voters are laser focused on beating Trump, Biden’s message has put him at an advantage, Kofinis said.



“For candidates like Sanders and Warren, they’ve got to convince a greater swath of Democrats that the country is ready to move further to the left, and that by moving further to the left you can win the general election,” he said.



Kofinis said that most Democratic voters have not yet committed to backing a particular candidate for the party’s nomination – 77 percent said that they are still undecided, according to the Park Street poll. But if either Sanders or Warren hopes to beat Biden in the primary contest, they will have to drum up support beyond their current bases of left-leaning voters, he said.



“The challenge that both of them have is that they’re arguably taking support from each other,” Kofinis said. “They’re not taking support from anyone else.”

-- Updated at 4:58 p.m.