NEW YORK (AP) -- The Democratic Party's left wing has warned for decades that America is moving toward an oligarchy in which a handful of billionaires controls much of the nation's wealth and political power.

President Joe Biden elevated such concerns from the Oval Office for the first time this week, just before he leaves office. In the hours that followed Biden's farewell address, progressives responded with a combination of appreciation, bemusement and frustration.

"Now he tells us," Sen. Sheldon Whitehouse, D-R.I., wrote on X, referring also to Biden's ideas for the U.S. Supreme Court. "Biden speaks out against dark money, for climate action, and for SCOTUS term limits. I pressed four years for this speech."

For much of the last four years, progressives were among Biden's biggest cheerleaders. And many remain supportive. But for others, the Democratic president's words were too little and far too late as the leader of a political party that has increasingly welcomed big-dollar donors even as it railed against President-elect Donald Trump's cozy relationships with others, tech titan Elon Musk chief among them.

The debate over the influence of billionaires in U.S. politics could have major implications for the policies that come out of Washington and the political landscape in future elections.

While Trump has cast himself as a fighter for the working class, the incoming Republican president is set to assemble the wealthiest presidential administration in history. He has tapped more than a dozen billionaires to take government posts, including Musk, the world's richest man, with a net worth exceeding $400 billion.

Meta CEO Mark Zuckerberg is co-hosting a reception with billionaire Republican donors next week for Trump's inauguration, the latest sign of the Facebook founder's embrace of the president-elect.

Democrats hope to undermine Trump's appeal with working-class voters by casting him as beholden to the billionaire class and trying to tie him to Musk, who once backed Biden and his Democratic predecessor, President Barack Obama.

According to the White House archives, Biden had not uttered the word "oligarchy" in the context of American politics until this week. And yet he made the influence of billionaires in U.S. politics a major focus of his final scheduled Oval Office address.

"Today, an oligarchy is taking shape in America of extreme wealth, power and influence that literally threatens our entire democracy, our basic rights and freedoms, and a fair shot for everyone to get ahead," Biden said with Vice President Kamala Harris and his family looking on. He pointed to "a dangerous concentration of power in the hands of a few ultra-wealthy people and the dangerous consequences if their abuse of power is left unchecked."

Few Democratic members of Congress criticized the outgoing president publicly, as Whitehouse did, but key figures in the party's far-left wing -- especially those close to independent Vermont Sen. Bernie Sanders -- were less cautious.

"It's cowardly that after representing the oligarchs for 50 years in office, he calls out this threat to our nation with just days left in his presidency," said Nina Turner, a national co-chair for Sanders' last presidential campaign. "(Biden) enabled, benefited from and emboldened the system that threatens us all, while he will ride off into the sunset and won't feel the harms of what's been built."

White House spokesman Andrew Bates pushed back against such criticism, noting that many party leaders praised the speech.

"President Biden's call to action resonated with a wide range of Democrats and others because it is in line with the values that, over these last four years, led to the most significant breakthroughs for working Americans since the New Deal," Bates said. "Like he said (on Wednesday), it's crucial to keep that flame lit and continue working against abuse of power by rich special interests and billionaires who want to profit ant the expense of American taxpayers."

Tiffany Muller, executive director of End Citizens United, a Democratic-aligned organization fighting to eliminate big money from politics, penned an op-ed Thursday describing Trump's inauguration next week as "the beginning of an oligarchy that's been 15 years in the making."

She acknowledged that the trend, enabled by the 2010 Supreme Court ruling for which her group is named that allowed wealthy donors to bypass political donation limits, is not exclusive to Trump's party.

"To be clear, Citizens United has allowed both parties to raise money from the billionaire class and large corporations. And Vice President Kamala Harris pulled in more total donations in the 2024 presidential race than her opponent did," Muller wrote. "But Trump is elevating his donors to major positions within the federal government."

Sanders, the self-described democratic socialist who has warned of a rising oligarchy in the United States for decades, thanked Biden for his choice of words. The Vermont senator cited the president again during a confirmation hearing for Trump's pick for Treasury Secretary Scott Bessent, a billionaire himself.

"What Biden said last night is that we're moving toward an oligarchy," Sanders said as he questioned Bessent. "Do you think that when so few people have so much wealth and so much political power that that is an oligarchic form of society?"

Bessent pushed back: "Well, I would note that President Biden gave the Presidential Medal of Freedom to two people who I think would qualify for his oligarchs."

Bessent was not wrong.

Biden earlier this month awarded the nation's highest civilian honor to Democratic megadonor George Soros and billionaire fashion magnate Ralph Lauren. And in the closing days of the presidential election, Harris' campaign elevated Mark Cuban, the billionaire owner of the Dallas Mavericks, as a top surrogate, though Cuban was not critical to her campaign the same way Musk was to Trump's with his advocacy on his X social media platform and his funding of pro-Trump super PACs.

Jeff Hauser, executive director of the Revolving Door Project, described "a sense of whiplash," suggesting that Biden is "desperate to placate" some billionaires while condemning others. Hauser said he wished that Biden's team and its allies on the center-left were as pugnacious over the last two years.

Faiz Shakir, a former Sanders campaign chief who launched a bid for Democratic National Committee chair earlier this week, said in an interview that Trump delivered a more compelling message to working-class voters in the last election at times. Shakir was critical of Cuban's role in the closing days of the election as well.

Marianne Williamson, who ran a long-shot presidential primary campaign against Biden and is now running for DNC chair, declined to give Biden credit for his latest remarks.

"This is news?" she said of the outgoing president's assessment. She added that America has been ruled by an oligarchy for years and called tech billionaires like Musk "Oligarchy 2.0."

Neither Shakir nor Williamson is considered a front-runner in the DNC chair's race. And those who are have been less critical of the influence of money in Democratic politics.

Elsewhere in the progressive movement, there was some appreciation that Biden raised concerns about oligarchy in American politics at all.

"Eisenhower's military-industrial complex warning gave language to an idea that has been referenced ever since," said Adam Green, co-founder of the Progressive Change Campaign Committee. "Biden's warning about oligarchs, calling on Americans to stand guard, is a call to action that will be felt for years."

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Cooper reported from Phoenix. AP writer Isabella Volmert in Detroit contributed.