During the 20th century extremist politics ravaged the lives of millions in Asia, Europe and Latin America. Americans were introduced to the phenomenon mostly in works of fiction, such as Sinclair Lewis’ 1935 satirical novel, “It Can’t Happen Here.”

But with Donald Trump now playing a leading role in U.S. politics, maybe it can happen here.

The right-wing extremists that Lewis satirized had gained power in Europe by appealing to the vulnerable and rightly aggrieved lower middle class who felt threatened by economic problems and erosion of the moral codes by which they lived. Christians, including prominent ministers, supported the extremists for the same reasons.

The politicians who exploited the vulnerable found scapegoats in so-called inferior people, among them Jews and Slavs, and in bankers and the wealthy. Above all, this extremism worshiped the exercise of power.

Donald Trump offers parallels to the right-wing extremists of 20th-century Europe. Trump typically speaks not of what is right or just, but of power and winning. He doesn’t scapegoat Jews, although he has dealt coyly with those who do, but doesn’t hesitate to target Muslims and Mexicans. He also doesn’t hesitate to bash Wall Street.

Despite past boasts of being a serial adulterer, Trump’s support among Christians is growing, as the Super Tuesday exit polls confirmed. Some prominent ministers have endorsed him. His appeal to power attracts those who feel themselves economically and culturally powerless.

Trump appears to have no real beliefs, conservative or otherwise. He has even at various times expressed support for policies with which the socialist Bernie Sanders could agree.

But that too fits the model of European extremism. Benito Mussolini, the founder of fascism, whom Trump has quoted with approval, began his political career as a socialist. Socialism of some sort was always a component of fascism (to take care of its vulnerable supporters), just as the exultation of power, governmental rather than personal, was always critical to socialism. Senator Sanders says the system is rigged to benefit the wealthy and he wants the power to smash it.

So Sanders, who speaks mainly of justice, and Trump, who speaks mainly of power, are in this sense strange extremist twins.

What allows extremists to arise and, in the case of Trump, thrive is disrespect for the rule of law.

“Progressives” often use the “fascist” pejorative to describe anyone who supports enforcing the rule of law. But the rule of law is the opposite of fascism, which above all is the assertion of power unconstrained by such bourgeois niceties as laws and constitutions.

Disrespect for the rule of law is growing in the United States. For some time, the Supreme Court has decided cases (abortion, same-sex marriage, gun rights, Obamacare), not based on what is written in the Constitution but on what a majority of the justices think is the right thing to do. Presidents, including George W. Bush and Barack Obama, have taken to issuing statements when signing laws that express their intent to modify the law through the executive branch’s enforcement of it. The American Bar Association has called this practice a threat to the rule of law and the constitutional separation of powers.

President Obama has broadened this practice and its harm by issuing executive orders mandating certain actions by government when Congress refuses to pass legislation he favors. Hillary Clinton has said she will continue this practice if elected president.

In such an environment, is it really a surprise that someone who unabashedly says that power is all that matters is thriving politically?

The rule of law is not perfect justice, but it is as close as we are likely to get. Americans can preserve our democratic republic by reverencing the law — and repudiating those who would replace its rule with their power.