With three years remaining in the presidency of Barack Obama, the party he has led since mesmerizing members with his 2008 campaign has begun debating a post-Obama future.

Though more united than Republicans, Democrats nevertheless face simmering tensions between the establishment and a newly energized populist wing, led by the unabashed liberalism of New York Mayor Bill de Blasio and the fiery rhetoric of Massachusetts Sen. Elizabeth Warren.

The schisms are as much stylistic as substantive. But however defined, they offer a challenge to the party’s next leader, whether former Secretary of State Hillary Rodham Clinton, Vice President Joe Biden or any number of lesser-knowns who await a decision by Clinton before making their own.

All will have to grapple with this reality. The Democratic Party, by various measures of public opinion, has moved to the left in the past decade. But that does not necessarily mean that progressives have become the party’s dominant force or that the policies and messages they advocate can carry the day in a national election.

“Nothing moves a party more than copying successful people,” said Andrew Stern, the former president of the Service Employees International Union, as he pointed to the prominence of de Blasio and Warren. “I think the party tends to drift in the direction of its successful innovators.”

Vice President Joe Biden blasted the GOP in a speech to Democrats Friday, insisting, "There isn't a Republican party." (The Associated Press)

But Stern cautioned that the bigger test of who holds power inside the party is proving those ideas can attract voters beyond staunchly liberal states or cities.

“It is fair to say that more liberal places find politicians first who are more willing to step out on these issues,” he said. “But it is not a shift until it’s seen to work in Minnesota or Wisconsin or New Mexico or Arizona.”

Adam Green, a co-founder of the Progressive Change Campaign Committee, a grass-roots group that has helped propel Warren’s rise, said the populist wing of the party is clearly ascendant.

“There’s been consensus in both parties since the 1990s Clinton days where big corporations run the show and both parties suck up to them and everything else falls into place from there,” he said. “The Elizabeth Warren wing really believes in challenging the current state of who has power and who has influence.

But other Democrats counter that the party must be careful about how it shapes its message and policies. Delaware Gov. Jack Markell, who came up through the centrist ranks of the party, noted that in the past when the progressive or liberal wings of the party were flourishing — he cited George McGovern’s candidacy in 1972 and Walter F. Mondale’s in 1984 — the party suffered major defeats.

“The idea of us as a party not continuing to understand where the people of the country are — we ignore all of that at our own peril,” he said.

How big a shift?

The Democratic Party of 2014 is one shaped both by the influences of former president Bill Clinton’s New Democrat ideas and the more liberal policy initiatives and cultural changes that have defined Obama’s presidency.

Obama’s tenure has intensified the debate over whether the Democrats are more ideologically liberal than they were a decade or two ago.

Conservatives see a president who has brought government much deeper into the health-care system, whose economic policies significantly increase the deficit and whose bent is for more government and more spending. But progressives see a president who lacks the populist edge they say the times demand and who has fallen short of the promise of his first campaign.

By many measures, the party is certainly seen as more liberal than it once was. For the past 40 years, the American National Election Studies surveys have asked people for their perceptions of the two major parties. The 2012 survey found, for the first time, that a majority of Americans describe the Democratic Party as liberal, with 57 percent using that label. Four years earlier, only 48 percent described the Democrats as liberal.

(In the same survey, 59 percent said they saw the Republicans as conservative, up from 52 percent four years earlier.)

Gallup reported last month that 43 percent of surveyed Democrats identified themselves as liberal, the high water mark for the party on that measurement. In Gallup’s 2000 measures, just 29 percent of Democrats labeled themselves as liberals.

Still, liberals are a plurality of the Democratic Party, not a majority, which is strikingly different from the Republican Party, where Gallup found that 70 percent identified themselves as conservative.

Joel Benenson, who was Obama’s lead pollster in 2008 and 2012, said Democrats are and always have been a progressive party, but they have balanced those ideas with practical policies that have attracted voters.

Asked about claims by some grass-roots progressives that the party is now Warren’s party, he said, “I don’t know what it means. Do you think that Harry Reid thinks it’s an Elizabeth Warren party? Do you think Chuck Schumer thinks it’s an Elizabeth Warren party? Do you think Hillary Clinton thinks it’s an Elizabeth Warren party? Do you think Barack Obama thinks it’s an Elizabeth Warren party? Or Nancy Pelosi?”

Democrats are most united on cultural and social issues, and it is here where the party has most obviously moved to the left, particularly on same-sex marriage and even the legalization of marijuana. But the party’s shift reflects overall changes in public attitudes that have kept the Democrats within a new political mainstream on these issues.

Women’s issues have provided even more cohesiveness within the party’s coalition.

“We’ve seen a gender gap for two decades now, but what we saw in 2012 was a larger step toward women voters standing with the Democrats in a much, much larger way,” said Stephanie Schriock, president of Emily’s List, a group that helps elect pro-choice Democratic women. “There’s such a contrast right now between the two parties on issues impacting women and families.”

On issues of national security and foreign policy, divisions remain. Obama may be president because he opposed the Iraq War and Clinton voted as senator to give then-president George W. Bush the authority to take the country to war. Obama has ended the war in Iraq and is ending the war in Afghanistan, but some progressives are at odds with him over other aspects of his national security policies.

Clinton may continue to disagree with part of her party’s base on these issues. Her record in the Senate and as Secretary of State is one where she has been, by evidence available today, fully supportive of the president’s drone policy and the National Security Agency’s surveillance policies.

Economic challenges

On economic issues, the party is torn between two key parts of its coalition.

“One of the biggest failings of the Democratic Party,” Stern said, “is that its funders come from its traditional side of the economic spectrum and its voters come from a more populist, distributive side of the economic agenda.”

Former Montana governor Brian Schweitzer said, “I think the party increasingly is responding to the special interests they need to get elected — the military-industrial complex, big energy, pharmaceutical companies, banks.”

Yet in both policies and tone, there are indications that Democrats have moved to the left. Democratic candidates from all regions — including two potential rising stars running for the Senate in conservative states, Michelle Nunn in Georgia and Alison Lundergan Grimes in Kentucky — have embraced raising the minimum wage. This is a centerpiece of Obama’s agenda heading into this fall’s midterm campaigns.

Democrats favor raising taxes on the wealthiest Americans, a rallying cry dating to the 1990s, but there are differences in the magnitude of tax increases and whom they would impact. New York is a microcosm. De Blasio and Gov. Andrew M. Cuomo both support expanding access to pre-kindergarten programs. But de Blasio wants to pay for it by raising taxes on the rich in New York City, while Cuomo objects to paying for universal pre-kindergarten through tax hikes.

Hostility to free-trade agreements is still deep among part of the Democratic coalition, but that tension has existed for decades. While many better-educated, upscale voters do not fear the impact of free trade, others, led by organized labor, look at stagnant wages and the difficult job market and attribute those hardships to trade.

Perhaps more than any other economic issue, income inequality has animated progressive activists and voters. Party strategists say this energy is being fueled by lingering fury at Wall Street tycoons, whom they blame for the financial collapse, and deep unease about the nation’s eroding middle class.

“There’s a consciousness developing that’s related to this issue of inequality and the unfairness of our system and the wealth gap that has the potential to really grow and develop into a strong movement that will be reflected in coming elections,” former Ohio governor Ted Strickland said.

William A. Galston of the Brookings Institution said, “It’s not just a case of the very rich getting richer. If that were the only thing going on I think we’d be having a very different conversation. It’s also a case of the people in the middle at best treading water and in fact doing a little bit worse than that.”

Warren, with her calls for tougher Wall Street regulations, and de Blasio, with his campaign mantle of “a tale of two cities,” have galvanized voters with fiery lines and fresh thinking.

“Part of it is really expanding the debate beyond the sterile ideas that have been in D.C. for a while,” Green said. “When the question was should we renew current interest rates for students or not, Elizabeth Warren said, wait, why is that the norm? Let’s give students the low rates that banks get, and she focused attention on the sweetheart deals we give the big guys.”

Obama and Senate Democrats running in difficult 2014 campaigns are adopting a more moderate approach — especially in rhetoric, style and emphasis. Where Warren speaks of economic justice and calls for Wall Street executives to be brought to trial, Obama talks, as he did in his State of the Union address last month, of expanding growth and opportunity.

Matt Bennett, a senior vice president at Third Way, a centrist think tank, said Obama’s approach is more resonant for more voters.

“What folks out in the country are trying to do is find a way to maintain their lifestyle,” he said. “Other than an intellectual exercise, they don’t see the struggle as focused on rich people. It is about their own situation and their own ability to make their way through a very difficult economy.”

Ohio Sen. Sherrod Brown, a leading liberal, said Democrats must not lose sight of their tradition as the party of progressive ideas.

“Fundamentally, there’s two things that elections and governing are all about — the future and whose side are you on,” he said. “Democrats win elections and govern well when we keep that front and center. . . . It’s always important to put some new face on this, and it matters how you dress it up, but fundamentally it’s the historic difference between the parties.”

Stern offered one caution to those on the left: “I think it’s really not helpful for the Democrats to turn this into an attack on the one percent. I don’t think it’s in the American spirit, or at least the Democratic Party’s future spirit. As Republicans attack immigration, we attack rich people? If you learned anything from the president, selling hope is better than selling hate.”

Looking ahead

For Democrats who could lead the party in the future, the challenge will be to articulate a new populist direction without denigrating the Obama record or abandoning the contributions of Bill Clinton. At the moment, Hillary Clinton is an overwhelming front-runner, and Democrats expect that, should she decide to run, she would define their party for the post-Obama era.

There is an assumption that if she faces a primary challenge in 2016, it would come from the left. Yet at this point, Clinton is as popular with the left in her party as with moderates and conservatives.

The most recent Washington Post-ABC News poll tested Clinton against other possible Democratic candidates and found 73 percent saying they favored her for the nomination. She had the backing of 74 percent of liberals, men, non-whites and those with college degrees. She had the support of 73 percent of moderates, women, whites and those without college degrees.

But that does not take away from the fact that Clinton would be under pressure to articulate a fresh economic vision to a party in which there is growing demand for a more populist edge to the rhetoric.

“The really interesting question is what changes in the political environment mean for the kind of economic policies she will advocate,” Galston said. “I don’t think she knows. . . . I’m pretty sure two things will not work: number one, pure undistilled populism; number two, a return to the centrist economics of the past. Neither of those is a formula.”

Some potential liberal primary challengers, like Schweitzer, are provocative but would have difficulty mounting a serious national campaign.

“Remember the song that was blaring when the Clintons took office? Fleetwood Mac, ‘Don’t stop thinking about tomorrow,’ ” Schweitzer said. “If we have a candidate that’s thinking about tomorrow, we’ll be very successful. If we have candidates that are the Beatles’ song ‘Yesterday,’ we won’t.”

Biden looms as a more serious potential candidate. He has been a key player in developing the Obama administration’s economic program. He oversaw the stimulus, led a middle-class task force and is focusing this year on job-training programs.

Beyond Clinton and Biden, however, the party has few elected officials with national standing. The 2010 elections cost the Democrats control of governorships in states including Ohio, Michigan, Wisconsin and Pennsylvania. That has left them with a more limited pool of candidates with executive experience and a record of action.

Governors often mentioned as possible candidates, especially with Clinton not in the race, include New York’s Cuomo, Martin O’Malley of Maryland and John Hickenlooper of Colorado. California’s Jerry Brown has already said he will not run in 2016.

Attention also could turn to a liberal like former Wisconsin senator Russell Feingold or a trio of female senators — Warren, Amy Klobuchar of Minnesota and Kirsten Gillibrand of New York. All three signed a letter last year saying they would support Clinton but would factor into the conversation if Clinton opts out.

One thing Democrats seem to agree on is this: If Clinton decides not to run, there will be chaos inside the party.

Scott Clement and Peyton Craighill contributed to this report.