Traditionally, American presidents have governed with dignity and a strong sense of national purpose and international responsibility. Since his election in 2016, however, Donald Trump has debased the dignity and decorum of the presidency.

Every day, over the past three years, he has trampled on the principles and practices of democratic governance. He caters to a disgruntled base of 35-40 percent of the U.S. population. What is conspicuously missing is any sense of public service or what might be called a moral conscience.

Instead of working for the country's best interests, Trump is out for himself and embellishing his name. Through words and deeds, Trump has shown himself to be a self-centered, divisive force.

As an American of Japanese ancestry, I am particularly troubled by Trump's cynical exploitation of racism. It is at the heart of his recent rants against four young Congresswomen of color, accusing them of being unpatriotic and telling them to "Go back to where you came from!"

When I have appeared for interviews on TV and radio many years ago to criticize America's unjustified internment of Japanese Americans, several listeners in the audience hollered that phrase at me. Never did I imagine, even then, that the president of the United States would stoop so low as to utter these demeaning words at four women of color recently elected to the U.S. Congress.

Bear in mind that "Go back to where you came from!" is never used against white Americans by minorities of color, such as blacks, Hispanics, or Asians. Why? Because minorities of color understand that farmers from Ireland, factory workers from Germany, and peasants from Russia are legitimate members of America's interwoven tapestry of immigration and social integration.

Of course, the same holds true for slaves brought over from Africa, railway workers from China, and farmers from Japan. But because immigrants of color -- and their American-born children -- are fewer in number than the majority population of whites, they tend to be looked down upon as illegitimate latecomers, outcasts, and socio-economic parasites, who receive free education and healthcare paid for by mainstream Americans.

In other words, "Go back to where you came from!" is the central slogan for an ideology of White supremacy. There is no place for such thinking in the dynamic diversity of American society. Under the U.S. Constitution, Americans of Japanese ancestry are completely equal to Americans of British or Irish ancestry.

The United States has been known as a safe harbor for immigrants. The Statue of Liberty is our national symbol, our historical identity. Inscribed on the statue are the words: "Give me your tired, your poor, your huddled masses yearning to breathe free."

As many white Trump supporters are dreading the day when people of color will outnumber them, Trump has played upon their fears, calling illegal immigrants from Mexico and Central America "gangsters, criminals, rapists, and drug dealers." Trump has ordered that children be separated from their parents once families have crossed the American border.

Tens of thousands of immigrants are now locked up in crowded detention centers that pointedly remind Americans of the grave injustice of imprisoning residents of Japanese ancestry in 1942.

Because the U.S.-Japan alliance is absolutely indispensable, Prime Minister Shinzo Abe has gone out of his way to cultivate a close relationship with Trump.

Yet, the U.S.-Japan alliance is sturdy enough to function effectively, even if the relationship between the two heads of state isn't cozy. It isn't necessary to curry favor with a president who will go down in history as a divisive and mendacious demagogue.

From my perspective as a second-generation Japanese American, I believe that the U.S.-Japan partnership is more than the sum of its economic and military parts. The U.S.-Japan alliance is, above all, a historic commitment to democratic values and institutions. To the extent that Trump tramples on, and poisons, the soil and soul of democracy, he is damaging the foundations of the U.S.-Japan partnership.

(Daniel Okimoto is a professor emeritus of Stanford University and co-chair of Silicon Valley Japan Platform. He was born in 1942 at the Santa Anita Race Track in California, which had been converted into a relocation facility for Japanese Americans. He was sent along with his family to the Poston War Relocation Center in Arizona and spent his early childhood there.)