Sen. Bernie Sanders, I-Vt., took aim on Wednesday at what he claimed was a Democratic Party “establishment that is working frantically to try and defeat us” and took repeated jabs at former Vice President Joe Biden as the battle for the Democratic presidential nomination crystallized into a two-candidate showdown.

Sanders - speaking to reporters in his home state of Vermont the day after Biden captured 10 of the 14 states holding primaries on Super Tuesday and overtook the populist senator in the all-important race for convention delegates – acknowledged that “it’s going to be pretty close. We may be up by a few. Biden may be up by a few. But we go forward neck and neck.”

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The senator – who’s making his second straight White House bid – zoomed to front-runner status after claiming partial victory in Iowa’s caucuses, winning New Hampshire’s primary outright, and then crushing his rivals in Nevada’s caucuses.

Biden – once the unrivaled front-runner in the race – nearly crashed and burned after disastrous performances in Iowa and New Hampshire. After finishing a distant second to Sanders in Nevada, Biden walloped him and the rest of the field in Saturday’s South Carolina primary. That ignited a tidal wave of support from a Democratic establishment that had become increasingly terrified of the prospect of Sanders – a self-described democratic socialist – as the party’s standard-bearer in November’s general election.

The former vice president was also aided by support from South Bend, Indiana Mayor Pete Buttigieg and Sen. Amy Klobuchar of Minnesota – both of whom dropped out of the race in the 48 hours before Super Tuesday and endorsed Biden. The former vice president overperformed on Tuesday – sweeping the southern contests as well as winning Minnesota, Massachusetts, Maine and the second biggest prize of the night – Texas. Biden’s surge spurred centrist candidate and former New York City Mayor Mike Bloomberg to suspend his campaign and back the former vice president on Wednesday morning.

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Sanders, who won the state with the most delegates – California – as well as Colorado and Utah and his home state of Vermont, told reporters that “I’m disappointed. I would like to win every state by a landslide" before launching a blistering attack on Biden for being beholden to wealthy donors and corporations.

Repeating his remarks to supporters the previous evening, Sanders slammed the former vice president over support for a “disastrous” trade deal, the bankruptcy bill, the Wall Street bailouts from 2008-2009, initially backing the war in Iraq, and pushing cuts to Social Security, Medicaid, Medicare, and veterans programs that Biden’s campaign dispute.

Sanders also spotlighted that the two rivals have “very different visions” on reforming health care, but emphasized that “I like Joe. He’s a decent guy" and hoped the two candidates could have a “serious” debate going forward and avoid what he termed “a food fight” at last week’s prime-time presidential primary debate in South Carolina.

He also defended one of three new ads his campaign’s running as of Wednesday in the March 10 and 17 primary states – which spotlights former President Barack Obama’s praise of the senator from Vermont.

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Since jumping into the race last April, Biden has repeatedly showcased his close working relationship as Obama’s right-hand man for eight years, and his campaign quickly took aim at the new spot.

Asked about the ad, Sanders told reporters that “I wanted to make it clear ... that I worked with him [Obama] and respected him." He also complimented the 44th president for staying neutral in the primary battle.

Looking ahead to Michigan – the largest prize next Tuesday, Sanders touted that ”we are going in there with the full expectation that we will win. Michigan is an extremely important state."

Sanders – who topped eventual nominee Hillary Clinton in 2016’s Michigan primary, stressed that voters there “were devastated by trade agreements” that he noted he opposed and that Biden supported.

Sanders spoke as his progressive supporters stepped up pressure on Sen. Elizabeth Warren to drop out of the race. Sanders’ fellow progressive champion and 2020 rival had an extremely disappointing night on Super Tuesday, notably finishing third in her home state of Massachusetts.

“We did speak on the phone a few hours ago,” Sanders acknowledged and said that Warren “is accessing her campaign.”

“She will make her own decision on her own time,” he added.

Biden camp calls out Sanders

About an hour before Sanders came before cameras, top Biden campaign officials criticized the senator for trying to divide the party by saying that the establishment “is teaming up to defeat him.”

On a conference call with reporters, Biden deputy campaign manager Kate Bedingfield called out the new Sanders TV commercials.

“He’s up this morning with three new attack ads, and you know, we all know, the stakes in this election and we need to unite to make Trump a one-term president,” she stressed.

The campaign – which struggled for 10 months with fundraising – touted that they saw a “tremendous surge in online fundraising.” But they wouldn’t say how much they raised in the hours after the Super Tuesday victories became apparent. Instead, they reiterated that Biden raised $15 million in the three days after South Carolina’s landslide.

And reacting to reports that there might be staffing changes at the campaign, Bedingfield said “any successful campaign is a growing campaign” and described them “as additions, not subtractions.”

Sanders, Biden, see room for improvement

Sanders was hampered on Tuesday by the lack of a surge in support from younger voters. For example, just 38 percent of the primary electorate in Virginia was between the ages of 18 and 44. That block favored Sanders over Biden by 40 percent to 33 percent. But among the 62 percent of Virginia voters 45 and older, just 13 percent backed Sanders, compared to 66 percent who went for Biden.

"Have we been as successful as I would hope in bringing in young people in? And the answer is 'no,’” Sanders admitted during his news conference.

"We’re making some progress but historically everybody knows that young people do not vote in the kind of numbers that older people vote," the senator added. "I think that will change in the general election. But to be honest with you, we have not done as well in bringing young people into the process. It is not easy.”

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Biden won big among African-Americans but fell far short against Sanders among Latino voters, who played an influential role in the California and Texas primaries. In Texas, Biden won African-American or black voters (who made up 20 percent of the primary electorate) 55 percent to 20 percent over Sanders. However, the Vermont senator beat Biden by 15 percentage points (41 percent to 26) among Hispanic or Latino voters, who made up 30 percent of the Texas electorate.

Los Angeles Mayor Eric Garcetti – a Biden campaign national co-chair admitted “we need to do more” to engage Spanish speaking voters.

Fox News' Andrew Craft contributed to this report.