The unsettled question of whether President Donald Trump is a threat to American democracy increasingly hinges on whether his words matter or not. Those who argue that Trump is an authoritarian can easily point to a nearly endless supply of evidence in the president’s tweets and off-the-cuff comments, notably in his repeated calls for the Department of Justice to investigate his political enemies.  

As Donald Trump tweeted on Jan. 2:

Donald J. Trump ✔ @realDonaldTrump
Crooked Hillary Clinton’s top aid, Huma Abedin, has been accused of disregarding basic security protocols. She put Classified Passwords into the hands of foreign agents. Remember sailors pictures on submarine? Jail! Deep State Justice Dept must finally act? Also on Comey & others

Aside from such blatant attacks on the rule of law, Trump’s own words convict him of being unfit in other ways, from his comments as a candidate that Mexican immigrants are rapists to his recent closed-door putdown of “shithole countries” while discussing Haiti, El Salvador, and African countries.
But using quotations to portray Trump as an extremist threat doesn’t convince everyone. There’s a formidable school of thought, encompassing analysts on the right and left, that Trump’s words don’t matter since they rarely manifest themselves in concrete, implemented policy. Trump might sound like an aspiring Mussolini, skeptical analysts argue, but in practice he’s no different than recent Republican presidents.
Ross Douthat, the conservative columnist for New York Times, argued last week that “angry presidential tweets that lack any sustained follow-through” are “not the same thing as a sustained presidential assault on democratic institutions.” Trump, the demagogue, has been tamed by the political system, he contends: “If the president yells about his persecutors and little or nothing happens—the Mueller probe continues, Rod Rosenstein keeps his job, etc.—what’s undermined is presidential authority, not the rule of law.”
Corey Robin, the leftist political scientist, has been making a similar argument for months. “Trump has always thought his words were more real than reality,” Robin wrote last May, having surveyed Trump’s paucity of policy achievements. “He’s always believed his own bullshit. It’s time his liberal critics stopped believing it.” More recently, he argued that “Trump is all bully, no pulpit,” and “that sometimes the main effect of Trump’s words is either nil or negative.”
Are Douthat, Robin, and others right in dismissing Trump as just a windbag? This view of Trump rests on a belief that political effectiveness is measured by legislative and other policy victories. But the office carries symbolic as well as legal power. As history shows, presidents have a real—if difficult to measure—ability to shape public discourse.
Jacob T. Levy, a political theorist at McGill University, convincingly made the case for the real-world impact of Trump’s words in a recent essay for the Niskanen Center. Drawing on the work of philosopher Hannah Arendt, Levy noted that political speech doesn’t exist in an abstract realm, but is a form of action—“the chief way in which we shape and constitute our life together.” Other political actors, including other nations and the American civil service, take cues from Trump’s words. It’s not a surprise, therefore, that Trump’s erratic language distresses allies like South Korea or provoked an exodus from the State Department.   
Trump is president, but also the standard bearer of the Republican Party, a position he’s embraced with the capriciousness of a feudal lord. As Levy notes, “over the last year Trump has successfully radicalized the Republican electorate, with his words, in their support of him personally. Congressional Republicans who, a year ago, were still at least trying to keep Trump at arm’s length don’t dare to anymore. Trump has successfully belittled, marginalized, and demonized his occasional critics among Senate Republicans, with his direct line to the Republican electorate (and, again, as always, its amplification in the Trumpist media).” 
Because of his high office, Trump shapes not just his own party, but also the opposition. Democrats and others opposed to Trump shape their politics as a negation of what he stands for. As Andrew Sullivan argues in New York magazine, “Polarization has made this worse—because on the left, moderation now seems like a surrender to white nationalism, and because on the right, white identity politics has overwhelmed moderate conservatism. And Trump plays a critical role. His crude, bigoted version of identity politics seems to require an equal and opposite reaction.”
Because the U.S. president is the head of state as well as the head of government, his words carry special weight in issues of national identity. As a settler country repeatedly infused by waves of immigration and the enforced migration of enslaved people, the United States has always asked itself, “What is an American?” History shows that presidents have had an outsized role in shaping the answer to that question with their words alone. One of the pivotal events in defining American identity was the Immigration Act of 1924, which sharply limited the number of immigrants admitted into the country and set up a quota system which privileged Northwestern European and Scandinavian countries over Southern European and Eastern European ones, while reducing African and Arab immigration to a trickle and excluding Asians entirely.
In the introduction to the 2006 essay collection Who Belongs in America? Presidents, Rhetoric, and Immigration, Vanderbilt University Communications professor Vanessa Beasley noted that the Immigration Act was shaped by the “inflammatory presidential discourse” of presidents who had left office long before 1924, notably Theodore Roosevelt and Woodrow Wilson. Roosevelt helped popularize eugenicist sentiments with a famous 1902 letter (which was reprinted in a book that same year), warning of the dangers of “race suicide” if “decadence and corruption” leads successful Americans to not have children. Although known as a proponent of the “melting pot,” Roosevelt’s attack on “hyphenated Americans” fueled nativist sentiments.
In a different essay in that collection, the historian Robert Ferrell wrote that Woodrow Wilson, in his five-volume History of the American People, “announced in its fourth volume that everything had been going well in the United States until the 1880s when there was a new immigration of people from Eastern Europe.” In 1916, as president, Wilson spoke against “immigrants who have poured the poison of disloyalty into the very arteries of our national life.”
In policy terms, the real impact of the words Roosevelt and Wilson uttered came after they were out of office. They paved the way for the 1924 Immigration Act, even if they didn’t live to see it.
The same power of presidential rhetoric can be seen in the Immigration and Nationality Act of 1965, which overturned the racist quota system in the 1924 act. The law was only made possible because of earlier presidents Harry Truman and Dwight Eisenhower, who challenged the public’s acceptance of the 1924 act and an equally xenophobic one in 1952. In policy terms, Truman and Eisenhower had paltry success: Congress overrode Truman’s veto of the 1952 act. But if they lost the short-term policy battle, Truman and Eisenhower won the long-term rhetorical battle. 
In vetoing the 1952 act, Truman said, “Today, we are ‘protecting’ ourselves, as we were in 1924, against being flooded by immigrants from Eastern Europe. This is fantastic.... We do not need to be protected against immigrants from these countries—on the contrary we want to stretch out a helping hand, to save those who have managed to flee into Western Europe, to succor those who are brave enough to escape from barbarism, to welcome and restore them against the day when their countries will, as we hope, be free again.” And in a speech that year, while running for president, Eisenhower described America as a nation open to all: “The whole world knows that to these shores came oppressed peoples from every land under the sun, that there they found homes, jobs and a stake in a bright, unlimited future.” 
“By defining immigration legislation as a tool of foreign policy,” historian James Aune wrote in Who Belongs in America?, “Truman and Eisenhower were able to lay the groundwork for the eventual elimination of the racist national origin restrictions of the 1924 and 1952 acts.”
Truman and Eisenhower teach the same lesson as Roosevelt and Wilson: The rhetorical power of the presidency has a ripple effect that lasts longer than one’s term in office. The implications for the present are clear. As Levy argues in his essay for the Niskanen Center (italics his, bold mine):
“Ignore the tweets, ignore the language, ignore the words” is advice that affects a kind of sophistication: don’t get distracted by the circus, keep your eye on what’s going on behind the curtain. This is faux pragmatism, ignoring what is being communicated to other countries, to actors within the state, and to tens of millions of fellow citizens. It ignores how all those actors will respond to the speech, and how norms, institutions, and the environment for policy and coercion will be changed by those responses. Policy is a lagging indicator; ideas and the speech that expresses them pave the way.
By empowering authoritarian and racist sentiments, and acclimatizing the Republican Party to accept those sentiments, Trump is reshaping American political discourse today in ways that could lead to reprehensible laws long after he’s left office.