Right after Sen. Bernie Sanders’s big win in last week’s Nevada caucuses, Joe Lockhart, President Bill Clinton’s former press secretary, expressed the fear gripping the Democratic establishment in an op-ed for CNN: “I don’t believe the country is prepared to support a Democratic socialist, and I agree with the theory that Sanders would lose in a matchup against Trump.”

Like much of the party establishment, he is viewing American politics through outmoded lenses of left versus right, with Sanders (I-Vt.) on the far left and President Trump on the far right. So-called moderates such as former New York mayor Mike Bloomberg and former South Bend, Ind., mayor Pete Buttigieg supposedly occupy the political center, appealing to a broader swath of the electorate.

This may have been the correct frame for politics decades ago, when America still had a growing middle class, but it’s obsolete today. As wealth and power have moved to the top and the middle class has shrunk, more Americans feel politically disempowered and economically insecure. Today's main divide isn’t left versus right. It’s establishment versus anti-establishment.

Some background: In the fall of 2015, I visited Michigan, Wisconsin, Ohio, Pennsylvania, Kentucky, Missouri and North Carolina, researching the changing nature of work for my book, “The System: Who Rigged It, How We Fix It.” I spoke with many of the same people I had met two decades prior, when I was secretary of labor, as well as some of their grown children. I asked them about their jobs and their views about the economy. I was most interested in their sense of our system as a whole and how they were faring in it.

What I heard surprised me. Twenty years before, most said they had been working hard and were frustrated that they weren’t doing better. Now they were angry — at their employers, the government and Wall Street; angry that they had not been able to save adequately for retirement, and that their children weren’t doing any better. Several had lost jobs, savings or homes during the Great Recession. By the time I spoke with them, most were employed, but the jobs hardly paid any more than they had years before.

I heard the phrase “rigged system” so often that I began asking people what they meant by it. They spoke about the bailout of the banks, political payoffs, insider deals and out-of-control CEO pay. The resentments came from self-identified Republicans, Democrats and independents; white, black, Latino and Asian American; union households and non-union. The common thread was that everyone was either middle or working class.

With the 2016 primaries on the horizon, I asked which candidates they found most attractive. At the time, party leaders favored Democratic former secretary of state Hillary Clinton or former Florida Republican governor Jeb Bush. But the people I spoke with repeatedly mentioned Bernie Sanders and Donald Trump. They said Sanders or Trump would “shake things up,” “make the system work again,” “stop the corruption” or “end the rigging.”

The next year, Sanders — a Jewish, 74-year-old Vermonter and self-described Democratic socialist — barely lost to Clinton in the Iowa caucuses, beat her decisively in the New Hampshire primary, garnered 47 percent of the caucus-goers in Nevada and ended up with 45 percent of the pledged delegates from Democratic primaries and caucuses.

Trump, then a 69-year-old egomaniacal maybe-billionaire and reality TV star who had never held office and never had any previous standing in the Republican Party, won the GOP primaries and then went on to beat Clinton (though not, of course, in the popular vote), one of the most experienced and well-connected politicians in modern America.

It was seismic, and it cannot be fully explained by Sanders’s or Trump’s appeal to their core base voters. It was a rebellion against the establishment. Clinton and Bush started with all the advantages, but neither could credibly convince voters they were not part of the system.

A direct line connected decades of stagnant wages, the 2008 financial crisis, the rise of the tea party and the occupy movement and the emergence of Sanders and Trump in 2016. The people I spoke with no longer felt they had a fair chance to make it. National polls told much the same story: According to the Pew Research Center, the percentage of Americans who felt most people could get ahead through hard work dropped by 13 points between 2000 and 2015. In 2006, according to Gallup, 59 percent of Americans thought government corruption was widespread; by 2013, 79 percent did.

Trump galvanized millions of blue-collar voters living in places that never recovered from the tidal wave of factory closings. He promised to bring back jobs, revive manufacturing and get tough on trade and immigration. “We can’t continue to allow China to rape our country, and that’s what they’re doing,” he roared. “Five, 10 years from now — different party. You’re going to have a workers’ party,” he forecast. “A party of people that haven’t had a real wage increase in 18 years, that are angry.” He blasted politicians and financiers who “took away from the people their means of making a living and supporting their families.”

Trump’s populist pose, of course, was one of the biggest cons in American political history. Since his election he has given the denizens of C-suites and boardrooms almost everything they’ve wanted and hasn’t markedly improved the lives of his working-class supporters, even if his politically incorrect, in-your-face style continues to make many feel as if he’s taking on the system.

The frustrations today are larger than they were four years ago. Even though corporate profits and executive pay have soared, the typical worker’s pay has barely risen, jobs are less secure, and health care less affordable.

The best way for Democrats to defeat Trump’s fake populism is with the real thing, coupled with an agenda of systemic reform. This is what Sanders offers. For that reason, he has the best chance of generating the energy and enthusiasm needed to regain the White House.

He will need a coalition of young voters, people of color and the white working class. He seems on his way: In Nevada, according to entrance polls, he won with Latino voters and white voters, women and men, college and non-college graduates. He was the first choice of every age group except for over-65. Nationally, he is narrowing former vice president Joe Biden’s edge with African American voters.

In a general election, Republicans would surely do everything they can to tag Sanders with the “socialist” label. But that hasn’t hurt him so far, partly because it doesn’t come with the stigma it once did.

And worries about a Nixon-McGovern-like blowout in 2020 seem far-fetched. In 1972, the middle class was expanding, not contracting. Polls currently show Sanders tied with or beating Trump: A Quinnipiac poll released last week shows Sanders beating Trump head-to-head in Michigan and Pennsylvania (but shows Trump beating all Democrats head-to-head in Wisconsin). A CBS News-YouGov poll released this week has Sanders beating Trump nationally.

Instead of hand-wringing about Sanders’s electability, maybe establishment Democrats should worry that a “moderate” Democrat might be nominated instead.