From the outset, several top-tier Democratic presidential candidates are pushing for new taxes on the wealthiest Americans and attempting to portray themselves as best positioned to fight the country’s yawning inequality gap.

It is an indication of how much the Democratic Party is shifting and how far the candidates are willing to go to appeal to the party’s energetic liberal faction. The debate over wealth – particularly with billionaires in the field and Democrats challenging a president whose riches helped get him to the White House – is a dominant theme of the early primary season.

Among the first advisers the candidates are consulting are not foreign affairs veterans or domestic policy experts, but economists.

Sen. Elizabeth Warren of Massachusetts is proposing a new “wealth tax” that would impose added levies on the 75,000 U.S. households with a net worth above $50 million. Sen. Kamala Harris of California – who also plans to unveil a proposal to increase taxes on the rich – wants to provide a tax credit of up to $500 per month to families making less than $100,000.

Sen. Bernie Sanders, I-Vt., who in his 2016 presidential run was an early advocate for higher taxes on the wealthy, introduced a bill Thursday to significantly increase the amount heirs would pay on the estates of their wealthy relatives. Under his plan, billionaires’ estates would be taxed at a 77 percent rate, and he would also lower the estate tax threshold to those inheriting $3.5 million.

The proposals reflect a broad shift in the mood of the Democratic Party and the country more generally, as the recent financial crisis and a distrust of big institutions has fueled a populist surge in both parties. A few years ago, Democrats were shifting to the center amid concerns they had drifted too far left, and emphasizing tax hikes was anathema; now some in the party are happy to call themselves socialists.

The tax plans are jump-starting a debate within the party over how far-reaching an overhaul should be, and they’ve prompted immediate criticism from moderates and wealthy potential candidates. The Democratic field could include several billionaires, and Howard Schultz, the former Starbucks chief executive who is considering an independent bid, has dismissed some of the tax plans as unrealistic while calling Warren’s “ridiculous.”

Others say that shows a failure to grasp the political moment.

“What’s ‘ridiculous’ is billionaires who think they can buy the presidency to keep the system rigged for themselves while opportunity slips away for everyone else,” Warren wrote on Twitter. “The top 0.1%, who’d pay my #UltraMillionaireTax, own about the same wealth as 90% of America. It’s time for change.”

Michael Bloomberg, the billionaire former New York mayor who is considering a run as a Democrat, said Warren’s plan is probably unconstitutional, adding that there is already a disturbing model for redistributing wealth.

“It’s called Venezuela,” he said during a recent trip to New Hampshire.

While Democrats have often favored increasing taxes on the wealthiest Americans, the latest proposals are pushing the limits of what was considered politically realistic just a few years ago. In the wake of the 2008 financial collapse, and a broad public sense that few of those responsible faced any consequences, liberal Democrats have increasingly focused on a broader overhaul of the system.

“It’s divisive between the classes, but that’s where we are in this point in time,” said Cornelius Hurley, a Boston University lecturer whose research has focused on the financial collapse. “Since the financial crisis, economic disparities have only gotten worse, not better. So Elizabeth Warren comes along and says, ‘Tax their wealth – not just their income, their wealth.’ ”

The reception of the various Democratic proposals will test just how much the mood has shifted and which candidate can project the right mix of anger and optimism.