Earlier this month, a revealing spat broke out on Twitter. David Sirota, a left-leaning journalist who once worked for Bernie Sandersannouncedthat he had uncovered something while mining campaign-finance data: “Beto O’Rourke is the #2 recipient of oil/gas industry campaign cash in the entire Congress.” Neera Tanden, the president of the Center for American Progress and a former domestic-policy adviser to Hillary Clinton and Barack Obama, pushed back. “Oh look,” she tweeted, “A supporter of Bernie Sanders attacking a Democrat. This is seriously dangerous.”

The dispute escalated three days later when The Washington Post’s Elizabeth Bruenig wrote a column declaring that she “can’t get excited about Beto O’Rourke” as a presidential candidate, because, among other things, he lacks a “well-attested antipathy toward Wall Street, oil and gas.” To which Tanden replied, “Bruenig’s piece in the Post on Beto is just the latest attack by a supporter of Senator Sanders.” Then, on December 10, the journal Sludge, which investigates money in politics, defended Sirota’s charge and noted that the Center for American Progress itself “has in the past accepted donations from multiple fossil fuel companies.”

On one level, the fight over O’Rourke is a fight over the legacy of Obama. The Obama veterans championing O’Rourke compare his “inspiration, aspiration, and authenticity” (in the words of Obama’s former campaign manager Jim Messina) to the 44th president’s. In a recent essay titled “The Case for Beto O’Rourke,” the former Obama aide Dan Pfeiffer declared that “the whole conversation around Beto has been eerily familiar to me, because these are the exact arguments people made to me when I told them I was considering working for Barack Obama 10 years ago.”

O’Rourke’s critics turn the analogy on its head. “Beto is a lot like Obama, true,” Bruenig acknowledges, but “it’s perhaps time for left-leaning Democrats to realize that may not be a good thing.” A recent Jacobin article called O’Rourke “Obama redux: an attractive, progressive-sounding, comforting figure” before declaring that Obama redux “would be disastrous,” given the former president’s policies on immigration, Wall Street, and war.

But the argument is about more than Obama. The people criticizing O’Rourke for taking fossil-fuel money don’t want to just prevent the Democratic Party from modeling its next presidential candidate on its last president. They want to overturn a model that has long dominated the party. Since the mid-20th century, Democrats have generally treated corporations as legitimate participants in the political process. Today, for the first time since the dawn of the Cold War, a powerful faction within the party wants to treat them as ideological adversaries instead.

Progressive democrats don’t talk a lot about William Jennings Bryan these days. But in important ways, he embodies the attitude toward corporations to which they’d like to return. In 1896, when the Democrats first nominated him for president, Bryan denounced “millionaires, who steal banks, mills, and railways,” “defaulters, who live in palaces and make away with millions,” and “money kings, who buy up Congress.” Bryan called American politics “a struggle between the idle holders of idle capital” and “the struggling masses, who produce the wealth and pay the taxes of the country.” Many corporations responded by sending their employees—along with their paychecks—“suggestions” that they vote for the Republican, William McKinley.

In Party Ideologies in America, 1828–1996, the University of Texas political scientist John Gerring argues that after Bryan’s loss “the accusation of illicit interference in the democratic process—via corporate contributions or employer coercion—would become a hallmark of Democratic campaigns” through the early-20th century. The party nominated Bryan for president twice more, in 1900 and 1908. And Gerring argues that Bryan’s antagonism toward corporations set a tone for Democratic leaders that continued—to varying degrees—through the 1940s. Woodrow Wilson, in 1912, warned that “the masters of the United States are the combined capitalists and manufacturers of the United States.” Franklin D. Roosevelt, in his 1936 inaugural address, boasted that “we have earned the hatred of entrenched greed,” and promised to battle the “political puppets of an economic autocracy.” Harry Truman, in 1948, savaged the “gluttons of privilege” from “Big Business” who “want a return of the Wall Street economic dictatorship.”

There were exceptions, of course. In the 1920s, the Democratic nominees James Cox and John W. Davis temporarily turned the party away from Bryan’s anti-corporate legacy. Roosevelt himself only fully embraced it after a few years in office, under pressure from populists such as Huey Long and Father Charles Coughlin. And Democrats expressed less class antagonism than many of their counterparts in Europe, where in the early-20th century socialist and labor parties rose to power.

Still, Gerring argues that in the half century between Bryan and Truman, Democrats were far more likely to depict corporations as ideological adversaries than they have been in the decades since. Starting in the 1950s, he argues, “the all-inclusive American People subsumed the figure of the Common Man. References to illicit business practices died out, to be replaced by a resolutely pro-business perspective. The organizing theme of Democratic ideology changed from an attack against special privilege to an appeal for inclusion.” One reason was the Cold War. With America facing a communist foe, it grew harder to fiercely challenge business without being accused of harboring sympathy for America’s enemies. Another was the legacy of the New Deal, which by empowering labor unions, regulating the economy, and expanding the social safety net reduced class anger.

Whatever the reason, Gerring argues that terms such as monopoly and speculation largely left the Democratic Party’s lexicon in the 1950s. The party’s tendency to see corporations as legitimate political actors continued even as the Chamber of Commerce and other business groups began an assault on taxation, regulation, and labor unions in the 1970s. It continued through the century’s end, even as that assault contributed to escalating income inequality. According to one profile, Tony Coelho, who ran the Democratic Congressional Campaign Committee from 1981 through 1986, “built his reputation by finding ways to entice business executives and their lobbyists to shower Democratic candidates with campaign cash.” In the 1990s, the Democratic Leadership Council, which included both Bill Clinton and Al Gore as prominent members, included on its executive committee Enron, Chevron, Philip Morris, Texaco, and Koch Industries. In 2008, Obama received almost twice as much money from employees of hedge funds and private-equity and investment firms as did John McCain. Former investment bankers served as three of his first four chiefs of staff.

What has occurred since then is a transition as potentially significant as the one the party underwent in the middle of the last century. It began with Sanders’s 2016 presidential campaign. Unlike Clinton in 2016 or Obama in 2012, Sanders ran without an allied super pac, leaving his supporters with no way to donate unlimited sums of money. Fifty-seven percent of his campaign money came via donations of fewer than $200, compared with 18 percent for Clinton. And Sanders made that distinction central to his campaign. He boasted that “we said ‘Hell no’ to super pacs. We don’t represent Wall Street or the billionaire class.” In debates, he slammed Clinton for giving paid speeches to Goldman Sachs. Yet despite eschewing corporate and Wall Street donors, Sanders raised roughly as much money as Clinton.

Since then, a growing number of Democrats in Congress have adopted Sanders’s model. Before 2016, accepting money from pacs funded by corporations wasn’t controversial in the Democratic Party. According to Adam Bozzi of the campaign-finance group End Citizens United, there wasn’t even an organized effort to ask candidates not to do so. After 2016, that began to change. By the start of 2017, eight Democrats in Congress had pledged to refuse corporate-pac money. When the new Congress convenes in January, the number will be 50. It will include Sanders, Elizabeth Warren, Cory Booker, and Kirsten Gillibrand, the four senators considered most likely to run for president, along with Beto O’Rourke.

Meanwhile, climate activists have begun pushing candidates to turn down not only donations from fossil-fuel pacs, but also those from fossil-fuel-company executives in excess of $200. According to R. L. Miller, the co-founder and political director of the super pac Climate Hawks Vote, the 115th Congress—which ends this year—contained 16 members who had signed the pledge. The incoming 116th Congress will contain 33. In 2017, Booker—who in 2014 received more money from the pharmaceutical industry than any other senator—announced that he would no longer take its money.

The demands for anti-corporate purity keep increasing. Activists close to Alexandria Ocasio-Cortez are now asking presidential contenders to pledge not to appoint Wall Street bankers to administration jobs.

Corporations still clearly enjoy influence inside the party. In June, the Democratic National Committee’s executive committee voted to reject moneyfrom pacs linked to the oil, gas, and coal industries, only to reverse course in August after claiming that labor unions had objected. But the very fact that the DNC had to depict its turnaround as a concession to labor suggests how dramatically the debate inside the party has changed. Leading Democrats may want to maintain their corporate and financial ties, but they are afraid to say so publicly. The days when a rising Democratic star such as Booker could call on his party—as he did in 2012—to “stop attacking private equity” are long gone.

What explains the change? One answer is the end of the Cold War. It’s easier to denounce corporations now that America is no longer waging a global struggle against a superpower that regularly denounced them itself. A second is income inequality. Unsurprisingly, the Democratic Party’s anti-corporate populism faded in the mid-20th century as government and labor checked corporate power, and it is now surging again because they no longer are. A third factor is climate change, which, as the push for a Green New Deal suggests, is becoming a defining issue for progressive activists. That has made it harder for Democratic politicians to accept money from oil, gas, and coal companies. Last week, Oregon’s Jeff Merkley, who declared himself “at war” with fossil-fuel companies, became the third senator to pledge to refuse money from their political-action committees and executives. “I have a feeling,” tweeted Bill McKibben of 350.org, “this is going to be a litmus test for Dems going forward.” The fourth answer is the internet, which has made it possible to raise vast sums of money without corporate help.

A fifth, less obvious answer is Donald Trump. By alienating well-off cultural moderates, Trump has allowed Democrats to gain ground among higher-income voters even as they adopt a more anti-corporate tone. It’s remarkable, when you think about it. Democrats lost voters who earn more than $100,000 by double digits in every national election from 1994 to 2004, when the DLC was at the height of its power. In 2016 and 2018, by contrast, the Democrats have lost these upper-income voters by only single digits, even as the party has grown more publicly critical of Big Business. If a more traditional Republican follows Trump—Nikki Haley, Mike Pence, Marco Rubio, Tom Cotton, or Ted Cruz—these two Democratic trends may collide. If they have another option, voters with economic views like Michael Bloomberg’s may not remain in a party whose economic message is shaped by Ocasio-Cortez.

In the 1930s and 1940s—when Democrats won big majorities among working-class whites—they didn’t need this upscale support. Nor was it difficult to balance issues of class and race, since most African Americans couldn’t vote. It’s far more challenging for the Democratic Party to keep its coalition together today.

The best hope for Democrats who don’t want to purge corporations from the party might be a presidential candidate with a less confrontational economic message who enjoys widespread African American or Latino support. Booker could be such a candidate. So could Kamala Harris or O’Rourke. Which is why skirmishes like the one that pitted the Center for American Progress’s Neera Tanden against supporters of Bernie Sanders will likely only escalate in the year and a half to come.