Liberal Democrats have been trying to get Warren, the senior senator from Massachusetts, to run for president for the better part of a year. Those vocal activists want a liberal option to push Hillary Clinton, the prohibitive favorite for the nomination but seen by some liberals as too politically moderate for their support.

Sanders, who is heading to New Hampshire for his first official campaign appearances on Saturday, wants to be that liberal option. His core positions -- breaking up Wall Street banks, making public college free, investing billions on infrastructure and guaranteeing health care for all -- are the same issues liberal groups have been championing for years. And his early campaign is starting to court organizers in key presidential states.

But as he settles into the Democratic presidential race, the response from some liberal groups and organizers has been markedly more focused on Warren, the middle-class champion and former Harvard professor, not Sanders, the Brooklyn-born, independent lawmaker with a gruff personality and an affinity for the moniker "democratic socialist."

Biden greets Sanders with an elbow bump before the start of a debate in Washington in March 2020. They went with an elbow bump instead of a handshake because of the coronavirus pandemic.

Biden greets Sanders with an elbow bump before the start of a debate in Washington in March 2020. They went with an elbow bump instead of a handshake because of the coronavirus pandemic.

Sanders speaks to reporters in Burlington, Vermont, a day after Super Tuesday II. Sanders said it "was not a good night for our campaign from a delegate point of view" but that he looked forward to staying in the race and taking on Joe Biden in an upcoming debate.

Sanders and former Vice President Joe Biden talk before a Democratic debate in Charleston, South Carolina, in February 2020.

Sanders and former Vice President Joe Biden talk before a Democratic debate in Charleston, South Carolina, in February 2020.

A triumphant Sanders raises his fist in San Antonio after he was projected to win the Nevada caucuses.

Sanders laughs during a primary-night rally in Manchester, New Hampshire, in February 2020. Sanders won the primary, just as he did in 2016.

In a tense and dramatic exchange moments after a Democratic debate, Warren accused Sanders of calling her a liar on national television. Sanders responded that it was Warren who called him a liar. Earlier in the debate, the two disagreed on whether Sanders told Warren, during a private dinner in 2018, that he didn't believe a woman could win the presidency.

US Rep. Alexandria Ocasio-Cortez introduces Sanders at a New York rally after endorsing him for president in October 2019.

US Rep. Alexandria Ocasio-Cortez introduces Sanders at a New York rally after endorsing him for president in October 2019.

Sanders campaigns at the University of New Hampshire in September 2019. A few days later, he took himself off the campaign trail after doctors treated a blockage in one of his arteries. Sanders suffered a heart attack, his campaign confirmed.

Sanders grabs the hand of US Sen. Elizabeth Warren during the Democratic debates in Detroit in July 2019.

Sanders grabs the hand of US Sen. Elizabeth Warren during the Democratic debates in Detroit in July 2019.

Sanders raises his fist as he holds a rally in Santa Monica, California, in July 2019.

Sanders raises his fist as he holds a rally in Santa Monica, California, in July 2019.

Sanders speaks next to former Vice President Joe Biden at the first Democratic debates in June 2019.

Sanders speaks next to former Vice President Joe Biden at the first Democratic debates in June 2019.

Sanders looks at his notes as he watches President Trump deliver the State of the Union address in February 2019. That month, Sanders announced that he would be running for president again.

Sanders looks at his notes as he watches President Trump deliver the State of the Union address in February 2019. That month, Sanders announced that he would be running for president again.

Sanders thanks supporters after winning re-election to the Senate in November 2018.

Sanders thanks supporters after winning re-election to the Senate in November 2018.

Sanders brings a giant printout of one of Donald Trump's tweets to a Senate debate in January 2017. In the tweet, Trump had promised not to cut Social Security, Medicare and Medicaid.

Sanders addresses delegates on the first day of the Democratic National Convention in July 2016.

Sanders speaks at a rally in Santa Monica, California, in June 2016. He pledged to stay in the Democratic race even though Clinton secured the delegates she needed to become the presumptive nominee.

Sanders speaks at a rally in Santa Monica, California, in June 2016. He pledged to stay in the Democratic race even though Clinton secured the delegates she needed to become the presumptive nominee.

Sanders speaks at a campaign event in New York's Washington Square Park in April 2016.

Sanders speaks at a campaign event in New York's Washington Square Park in April 2016.

Sanders speaks at a campaign rally in Ann Arbor, Michigan, in March 2016. He won the state's primary the next day, an upset that delivered a sharp blow to Clinton's hopes of quickly securing the nomination.

Sanders and his wife, Jane, wave to the crowd during a primary night rally in Concord, New Hampshire, in February 2016. Sanders defeated Clinton in the New Hampshire primary with 60% of the vote, becoming the first Jewish candidate to win a presidential primary.

Comedian Larry David and Sanders appear together on "Saturday Night Live" in February 2016. David had played Sanders in a series of sketches throughout the campaign season.

Sanders sits with rapper and activist Killer Mike at the Busy Bee Cafe in Atlanta in November 2015. That evening, Killer Mike introduced Sanders at a campaign event in the city. "I'm talking about a revolutionary," the rapper told supporters. "In my heart of hearts, I truly believe that Sen. Bernie Sanders is the right man to lead this country."

Sanders waves while walking in a Veterans Day parade in Lebanon, New Hampshire, in November 2015.

Sanders waves while walking in a Veterans Day parade in Lebanon, New Hampshire, in November 2015.

Sanders embraces Remaz Abdelgader, a Muslim student, during an October 2015 event at George Mason University in Fairfax, Virginia. Asked what he would do about Islamophobia in the United States, Sanders said he was determined to fight racism and "build a nation in which we all stand together as one people."

Sanders embraces Remaz Abdelgader, a Muslim student, during an October 2015 event at George Mason University in Fairfax, Virginia. Asked what he would do about Islamophobia in the United States, Sanders said he was determined to fight racism and "build a nation in which we all stand together as one people."

Seconds after Sanders took the stage for a campaign rally in August 2015, a dozen protesters from Seattle's Black Lives Matter chapter jumped barricades and grabbed the microphone from the senator. Holding a banner that said "Smash Racism," two of the protesters -- Marissa Johnson, left, and Mara Jacqueline Willaford -- began to address the crowd.

In July 2015, two months after announcing he would be seeking the Democratic Party's nomination for President, Sanders spoke to nearly 10,000 supporters in Madison, Wisconsin. "Tonight we have made a little bit of history," he said. "You may know that some 25 candidates are running for President of the United States, but tonight we have more people at a meeting for a candidate for President of the United States than any other candidate has."

In March 2015, Sanders speaks in front of letters and petitions asking Congress to reject proposed cuts to Social Security and Medicare.

In March 2015, Sanders speaks in front of letters and petitions asking Congress to reject proposed cuts to Social Security and Medicare.

Sanders and US Rep. Jeff Miller, chairman of the House Committee on Veterans' Affairs, walk to a news conference on Capitol Hill in 2014. Sanders was chairman of the Senate Committee on Veterans' Affairs.

Sanders and US Rep. Jeff Miller, chairman of the House Committee on Veterans' Affairs, walk to a news conference on Capitol Hill in 2014. Sanders was chairman of the Senate Committee on Veterans' Affairs.

Sanders speaks to reporters in 2010 about the Obama administration's push to extend Bush-era tax cuts. Three days later, Sanders held a filibuster against the reinstatement of the tax cuts. His speech, which lasted more than eight hours, was published in book form in 2011. It is called "The Speech: A Historic Filibuster on Corporate Greed and the Decline of Our Middle Class."

Sanders speaks to reporters in 2010 about the Obama administration's push to extend Bush-era tax cuts. Three days later, Sanders held a filibuster against the reinstatement of the tax cuts. His speech, which lasted more than eight hours, was published in book form in 2011. It is called "The Speech: A Historic Filibuster on Corporate Greed and the Decline of Our Middle Class."

Sanders chats with Dr. John Matthew, director of The Health Center in Plainfield, Vermont, in May 2007. Sanders was in Plainfield to celebrate a new source of federal funding for The Health Center.

Sanders chats with Dr. John Matthew, director of The Health Center in Plainfield, Vermont, in May 2007. Sanders was in Plainfield to celebrate a new source of federal funding for The Health Center.

Sanders takes part in a swearing-in ceremony at the US Capitol in January 2007. He won his Senate seat with 65% of the vote.

Sanders takes part in a swearing-in ceremony at the US Capitol in January 2007. He won his Senate seat with 65% of the vote.

Barack Obama, then a US senator, endorses Sanders' Senate bid at a rally in Burlington in 2006.

Barack Obama, then a US senator, endorses Sanders' Senate bid at a rally in Burlington in 2006.

Sanders sits next to President Bill Clinton in 1993 before the Congressional Progressive Caucus held a meeting at the White House. Sanders co-founded the caucus in 1991 and served as its first chairman.

Sanders sits next to President Bill Clinton in 1993 before the Congressional Progressive Caucus held a meeting at the White House. Sanders co-founded the caucus in 1991 and served as its first chairman.

In 1990, Sanders defeated US Rep. Peter Smith in the race for Vermont's lone House seat. He won by 16 percentage points.

In 1990, Sanders defeated US Rep. Peter Smith in the race for Vermont's lone House seat. He won by 16 percentage points.

Sanders reads mail at his campaign office in Burlington in 1990. He was running for the US House of Representatives after an unsuccessful bid in 1988.

Sanders reads mail at his campaign office in Burlington in 1990. He was running for the US House of Representatives after an unsuccessful bid in 1988.

In 1987, Sanders and a group of Vermont musicians recorded a spoken-word folk album. "We Shall Overcome" was first released as a cassette that sold about 600 copies. When Sanders entered the US presidential race in 2015, the album surged in online sales. But at a CNN town hall, Sanders said, "It's the worst album ever recorded."

Sanders, right, tosses a baseball before a minor-league game in Vermont in 1984. US Sen. Patrick Leahy, center, was also on hand.

Sanders, right, tosses a baseball before a minor-league game in Vermont in 1984. US Sen. Patrick Leahy, center, was also on hand.

Sanders takes the oath of office to become the mayor of Burlington, Vermont, in 1981. He ran as an independent and won the race by 10 votes.

Sanders takes the oath of office to become the mayor of Burlington, Vermont, in 1981. He ran as an independent and won the race by 10 votes.

Sanders, right, leads a sit-in organized by the Congress of Racial Equality in 1962. The demonstration was staged to oppose housing segregation at the University of Chicago. It was Chicago's first civil rights sit-in.

Sanders, right, leads a sit-in organized by the Congress of Racial Equality in 1962. The demonstration was staged to oppose housing segregation at the University of Chicago. It was Chicago's first civil rights sit-in.

US Sen. Bernie Sanders speaks at a campaign rally in Chicago in March 2019. Sanders, an independent from Vermont, is the longest-serving independent in the history of Congress.

US Sen. Bernie Sanders speaks at a campaign rally in Chicago in March 2019. Sanders, an independent from Vermont, is the longest-serving independent in the history of Congress.

Anna Galland, executive director of MoveOn.org Civic Action, welcomed Sanders into the race and touted his record on Wednesday before noting that the Vermont-based Move On and their allies would "continue to call on Sen. Elizabeth Warren to also bring her tireless advocacy for middle-class and working Americans to the race."

Democracy for Action, another liberal group whose views track closely with Sanders, had a similar reaction.

Our "members are excited to have progressive champion Senator Bernie Sanders join the 2016 presidential race," said Charles Chamberlain, the group's executive director, before adding, "We continue to encourage Senator Elizabeth Warren to join the race for president."

Both Move On and Democracy for America have dumped millions into a campaign urging Warren to run. But with every interview the Warren does, that goal looks less likely.

"I am not running and I am not going to run," Warren bluntly said in March

The dynamic of liberal groups lining up behind a candidate who says she isn't running quietly bothers some Sanders' aides. They look at the money groups are spending to draft Warren and can't help but think about what that money could do for them.

"Obviously, one would hope one would have as much support as possible from all walks of life," Sanders said earlier this year when asked why he thinks groups like Move On aren't rallying around him. "I am a great fan of Elizabeth, and as for what people do and why they don't do it, I am not going to speculate."

Tad Devine, one of Sanders' top campaign advisers, said Thursday that he isn't particularly bothered by the clamoring for Warren because "she isn't going to run for president."

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"There are a lot of people out there who are looking for someone like Elizabeth Warren and are really interested in those issues," Devine said. "I think when Bernie starts talking about those issues in his own way, it is going to be a lot easier for someone like him to get their support, than someone like Clinton, O'Malley, Webb or Link Chaffee."

Devine added: "I view those people as tremendous targets of opportunities for a candidate like Bernie Sanders."

Although liberal organizations aren't backing Sanders, he does have a small but devout following in places like Iowa and New Hampshire, critical states in the presidential nomination process. Sanders regularly draws well at small house parties and town halls across both states, bringing out people who see him as their Clinton alternative.

A majority of Democratic voters, though, don't feel this way. In a March CNN/ORC poll, Sanders garnered 3% of the vote compared to Warren's 10%. When you remove Warren from the poll, Sanders jumps by 2 points to 5%, but Clinton jumps by 5 points to 67%.

"I like his views, I like him a lot," said Timothy Horrigan, a liberal New Hampshire representative, before listing all the ways Bernie isn't Elizabeth.

"She is more plausible as a president," Horrigan said. "They have similar messages but they have different styles, and her style appeals to a lot of people. She is sort of like Hillary without all the baggage and just a stronger progressive message."

Many in the progressive movement are uncomfortable with questions about why they are supporting Warren over Sanders.

Photos: Alternatives to Hillary Clinton 2016 Photos: Alternatives to Hillary Clinton 2016 Jim Webb: "I look forward to listening and talking with more people in the coming months as I decide whether or not to run." Hide Caption 1 of 10 Photos: Alternatives to Hillary Clinton 2016 Joe Biden: "That's a family personal decision that I'm going to make sometime at the end of the summer." Hide Caption 2 of 10 Photos: Alternatives to Hillary Clinton 2016 Martin O'Malley: "I've been very encouraged as I travel around the country by a number of people who repeat again and again and again their desire for getting things done again as a country and also for new leadership to get those things done." Hide Caption 3 of 10 Photos: Alternatives to Hillary Clinton 2016 Elizabeth Warren: "I'm not running for president....I don't get who writes these headlines or what they're about. I think there's just kind of a pundit world out there." Hide Caption 4 of 10 Photos: Alternatives to Hillary Clinton 2016 Jerry Brown: "If no one runs and [everyone] says we'll have an absent Democratic nominee, would I rule that out? I mean, that would be a little silly, wouldn't it?" Hide Caption 5 of 10 Photos: Alternatives to Hillary Clinton 2016 Former Rhode Island Governor Lincoln Chafee is a one-time Republican, turned independent, now Democrat and is exploring a run for the presidency. On Hillary Clinton, he told CNN "... anybody who voted for the Iraq War should not be president and certainly should not be leading the Democratic Party." Hide Caption 6 of 10 Photos: Alternatives to Hillary Clinton 2016 Bernie Sanders: "I haven't made up my final decision and I've got to say a lot of my strongest supporters say, 'Bernie, you've gotta stay out of the damn Democratic Party, run as an Independent." Hide Caption 7 of 10 Photos: Alternatives to Hillary Clinton 2016 Kirsten Gillibrand: The New York senator has said she'll support Hillary Clinton "110 percent." Hide Caption 8 of 10 Photos: Alternatives to Hillary Clinton 2016 Andrew Cuomo (in 2014): "I'm focusing on running for governor. And then I'm going to focus on being the best governor I can be." Hide Caption 9 of 10 Photos: Alternatives to Hillary Clinton 2016 Brian Schweitzer: When asked by Time if he would be a better candidate for president than Clinton: "Well, I think so, of course. I think I have a background and a resume that isn't just in government." Hide Caption 10 of 10

"We don't have more to say beyond the statement I sent earlier," a spokesman for Move On said after CNN asked a number of questions on the issue.

There is some hope in the liberal movement that the focus on Warren and the issues she represents will help Sanders, too.

Adam Green, co-founder of the Progressive Change Campaign Committee, said Wednesday that Warren "has been a galvanizing force for economic populism" and is someone who is "symbolic of the rising economic populist tide in America."

"Those are just the facts," the liberal organizer added.

By implication, though, Sanders is not that. Though Green said the independent senator is "very much in line with the goal that many progressives have," he acknowledged that Sanders' 2016 campaign would need to ride the "economic populist tide" that Warren symbolizes for many liberals.

"The rising economic populist tide can be ridden by many people," he said. "And I think that any politician who is smart will try to ride that tide."