What has happened to Republicans that Donald Trump, after Super Tuesday, is their presumptive candidate for president?

Trump is revitalizing an old American political movement — populist nationalism.

Trump speaks for those deeply hurt by the rise of the left, who feel marginalized. Who resent that their country has been let down and trashed by the rich and the well-educated.

Trump can't be seen as leading established conservatives. He is a populist, not a conservative, and there is a big difference.

This new disposition of mostly white, middle-class and lower-middle-class Americans is a resurgence of an old theme in American life. We haven't called it "populism" in a long time. And rightly so, for it is the core of what was once called "Americanism."

Frankly, it is a kind of old-fashioned, 19th-century "liberalism" under which free markets and limited government are trusted to help individuals rise in life. The "liberalism" denotes individuals' liberty to make the most of their opportunities. That is the idea of America.

Trump and his supporters don't want to "conserve." They want change, not the status quo. They want to "win," not "lose." They want the good life and are willing to work for it, playing by the rules of free-market competition and bottom-up politics. They see themselves as the remaining true believers in the American Dream.

Trump's supporters echo the tradition of Americanism stretching back to the Puritans and the Revolution, to people who came to America seeking religious freedom or other personal opportunity or who were born here and understood the country to be open for growth and development and personal advancement.

Our nationalism, as has often been said, has always been different from the solidarity of other countries. Its idealism is not based on a single religious, racial or ethnic heritage. Americanism as a cause to live and die for is a set of ideas open to any who believe in them.

After the Revolution secured autonomy for American nationalism, Andrew Jackson rallied this sentiment among those resentful of the East Coast gentry Federalists. Then Lincoln, also from the frontier, mobilized it again in the Republican Party, advocating social advancement through free labor.

After the Great Depression, the banner of fair access to opportunity was picked up by Franklin Roosevelt. In his footsteps came Lyndon Johnson from the Texas Hill Country. Later, the cause was championed by Ronald Reagan.

Now it is in the hands of Donald Trump.

Like those who fashioned the Constitution, Lincoln thought positively of government. As he said, government is there to do for us what we cannot do for ourselves. Subservient to the people, American government was to serve their aspirations.

As a populist, Trump — like Lincoln — does not disparage government the way our recent conservative movement has. Trump and his followers understand that government needs to put institutions in place that will help individuals prosper on their own. This is perhaps the biggest difference between American populists and conservatives.

Whoever or whatever will trod on opportunity for average Americans will earn the ire of Donald Trump — be it illegal immigration, hedge-fund millionaires or unctuous government regulators.

We must not overlook the fact that the social resentment of elites mobilizing behind Trump is boosting Democrat Bernie Sanders as well. Sanders, though, is more limited in his understanding of Americanism: He puts most responsibility on government to fund entitlements as the road to self-improvement, little on individuals to make it on their own.

Trump's populism is ascendant because the conservative movement has morally collapsed. It has become a stodgy establishment, too self-interested and pontifical.

The conservative movement broke out of marginal cultural dyspepsia with Barry Goldwater's 1964 campaign for the presidency. Under the guidance of the writer Russell Kirk, Goldwater allowed himself to be presented as a "conservative."

Kirk and his associate William Buckley, founders of the National Review magazine, were indeed conservatives, not populists. Such conservatives sought a culture of hierarchy and duty, opposing the egalitarian individualism of modernity. They believed in conforming to the unchanging law of human nature and its necessary social structures.

Buckley was a proud Catholic, and Kirk converted to Catholicism toward the end of his life. Catholic thought — going back to the Counter-Reformation and St. Thomas Aquinas — is very conservative, arguing that every individual has a place in God's order and our vocation is to stay in our places with gratitude.

Intellectually at odds with American individualism, the conservative elite had to piggyback on middle-class populism.

Richard Nixon mastered this marriage of convenience, building his following on American nationalism in its fear of Communist aggression. He also embodied small-town values of traditional morality and upward mobility. In 1968, he saw the opportunity to broaden his coalition by reaching out to the white South, which resented the "oppressiveness" of the federal government in Washington.

Ronald Reagan, too, was really a national populist touting the values of Americanism. Reagan brought reassurance that America would defeat communism and protect its middle-class heritage of cautious-but-steady upward mobility and old-time family values.

Since Reagan, the self-righteous conservative movement has managed to mobilize only a minority of Americans on a consistent basis. This is not much to show for 50 years of intense proselytizing and the raising of untold millions of dollars.

Trump's campaign has revealed conservatism as a hollow shell out of touch with a majority of Americans.

Populism and its faith in the American Dream, however, is here to stay.

Stephen B. Young, of St. Paul, is global executive director of the Caux Round Table, an international network of business leaders working to promote a moral capitalism.