BERKELEY — On Tuesday, an impeached president who is up for re-election delivered a State of the Union address to the most divided union in living memory.

But why are we so divided? Part of the answer is Trump himself. The Great Divider knows how to pit native-born Americans against immigrants, the working class against the poor, whites against blacks and Latinos, and evangelicals against secularists. Trump thrives off disruption and division.

But that begs the question of why we have been so ready to be divided by Trump. The answer derives in large part from what has happened to wealth and power in America.

In the fall of 2015, I spoke with many of the people I had met 20 years before when I was secretary of labor, as well as with some of their grown children.

They were angry at their employers, the government, Wall Street. Many had lost jobs, savings or homes in the Great Recession following the financial crisis of 2008, or knew others who had. Most were back in jobs, but the jobs paid no more than they had two decades before, in terms of purchasing power.

They spoke about a “rigged system” that delivered flat wages, shrinking benefits, growing job insecurity. They talked about the bailout of Wall Street, political payoffs, insider deals, soaring CEO pay and “crony capitalism.”

With the 2016 primaries looming, I asked which candidates they found most attractive. At the time, the leaders of the Democratic party favored Hillary Clinton, and Republican leaders favored Jeb Bush. Yet no one I spoke with mentioned Clinton or Bush.

They talked instead about Bernie Sanders and Donald Trump. When I asked why, they said Sanders or Trump would “shake things up” or “make the system work again” or “end the rigging.”

In the following year, Sanders ended up with 46 percent of the pledged delegates from the Democratic primaries and caucuses, and Trump went on to beat Clinton.

Something very big had happened, and it wasn’t due to Sanders’ magnetism or Trump’s likability. It was a rebellion against the establishment. That rebellion continues, although much of the establishment still denies it.

Trump galvanized millions of blue-collar voters living in communities 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 said at one rally. “In five, 10 years from now, you’re going to have a workers’ party. A party of people that haven’t had a real wage increase in 18 years, that are angry.”

Speaking at a factory in Pennsylvania in June 2016, Trump decried politicians and financiers who had betrayed Americans by “taking away from the people their means of making a living and supporting their families.”

Democrats had occupied the White House for 16 of the 24 years before Trump’s election and in that time had scored some important victories for working families: the Affordable Care Act, an expanded earned income tax credit and the Family and Medical Leave Act. I take pride in having been part of a Democratic administration during that time.

But Democrats did nothing to change the vicious cycle of wealth and power that rigged the economy for the benefit of those at the top and undermined the working class. As Democratic pollster Stanley Greenberg concluded after the 2016 election, “Democrats have lost support with all working-class voters across the electorate.”

A direct line connects the four-decade stagnation of wages with the bailout of Wall Street, the rise of the tea party (and, briefly, Occupy Wall Street), and the successes of Sanders and Trump in 2016.

The most powerful force in American politics today continues to be anti-establishment fury at a rigged system. There is no longer left or right. There’s no longer a moderate “center.” There’s either Trump’s authoritarian populism or democratic — small “d” — populism.

Trump has harnessed the frustrations of at least 40 percent of America. Although he’s been a Trojan horse for big corporations and the rich, giving them all the tax cuts and regulatory rollbacks they’ve sought, the working class continue to believe he’s on their side.

Democrats cannot defeat authoritarian populism without an agenda of radical democratic reform, an anti-establishment movement. They must stand squarely on the side of democracy against oligarchy.

Trump is not the cause of our divided nation. He is the symptom of a rigged system that was already dividing us. It’s not enough to defeat him. We must reform the system that got us Trump in the first place.

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Robert Reich’s new book, “The System: Who Rigged It, How We Fix It,” will be out in March.