My grandparents sailed through the harbor of hopes and dreams nearly a century ago. They knew too well the pain and sadness they left behind; less clear was what would await them here where “the streets were paved with gold.”

What they found was, in a word, complicated.

A vibrant Jewish world already had been created. As advertised, it was, to their delight, quite different from Poland. Simply put, they felt like they could breathe here. They felt free.

That said, anti-Semitism was easily found. Just a few years before they came to Ellis Island, Leo Frank had been lynched by a mob in Georgia.

Two years later, at midnight on Thanksgiving 1915, a small group of men ignited a wooden cross and declared the rebirth of the Ku Klux Klan, an organization of xenophobic hate and violence that would flourish in the decade that followed.

As my grandparents arrived, the country had just elected a new president. Warren G. Harding ran on an “America First” platform. He was highly critical of foreign entanglements, the “do-gooder” proclivities of his predecessor, Woodrow Wilson, and the progressivism of Teddy Roosevelt. Representing an isolationist mood that was distrustful of foreigners, Harding presided over a steep restriction of immigration. The times were known as “the tribal ’20s.”

One of Harding’s supporters, Henry Ford, published “exposés” of Jewish conspiracies, gleaned from “The Protocols of the Elders of Zion.” Prominent universities, led by Harvard, established strict quotas to limit the (alarming) growth of Jewish students. And, of course, had my grandparents imagined moving to certain neighborhoods or joining social clubs, they’d have faced restrictions.

None of this put a dent in the love affair between my grandparents and their adopted country. Whatever prejudice they experienced felt small compared with what they left behind — as we sat watching the pogrom scene in “Fiddler on the Roof,” my grandmother said, unimpressed, “This they call a pogrom?”

There were enormous differences. While we can say that American anti-Semitism of a century ago was pervasive and institutionalized, my grandparents could distinguish it from the anti-Semitism of their youth that was supported (openly or tacitly) by the authorities. Here, when Gen. Ulysses S. Grant tried to expel Jews from western Tennessee, President Lincoln rescinded the order — not because Lincoln was fond of Jews, but because it violated their constitutional rights.

The anti-Semitism that rippled across America as my grandparents arrived was no coincidence. More than 20 million immigrants came between 1881 and 1924, when the doors closed. Two million were Jews.

The influx, along with the first wave of the Great African American Migration, not to mention first-wave feminism (women got the vote in 1919), profoundly changed the country and deeply unsettled those whose image of America was overwhelmingly white, Anglo-Saxon, Protestant and male. Recession-fueled economic anxiety fused with fear that the new “melting pot” was changing the religious, racial and cultural character of the country. All this made for a potent mix of xenophobia, white supremacy and anti-Semitism.

Jews survived the Harding era and thrived. Looking back, the American Jewish experiment has been a resounding success by almost every measure. Jews have advanced politically, socially, culturally, educationally and economically. The discrimination that targeted my grandparents’ and my parents’ generations had largely disappeared by the time the baby boomers came of age.

And yet …

For the first time since Harding, an “America First” administration again resides in the White House, representing, as then, distrust of foreign entanglements and foreigners. As then, Jews observe, with discomfort, escalation of anti-Semitism and xenophobia. As then, conspiracy theories abound, this time suggesting Jews were behind the slave trade, the spread of AIDS, the 9/11 attack, the refugee caravans. As then, people are angry and frightened by change. And, as then, Jews are frightened by the ugly reactions spawned by that fear and anger.

Historian Jonathan Sarna cites three strategies American Jews employed in the ’20s to defend their interests:

1. They supported each other.

2. They fought back.

3. They allied with others in the battle against hatred.

A hundred years ago, American Jews were primarily concerned with defending themselves and their interests. Today, Jews view their relationship with America on a different footing. Jews in our community express at least as much concern about defending democratic norms and institutions, and not simply because it is “good for the Jews.” Rather, they see it as their responsibility as Americans.

I’d add two grace notes:

“Supporting each other” requires not succumbing to the political tribalism rampant in today’s America. If we don’t like the name-calling and ad hominem attacks that dominate the headlines, we must model alternative modes of discourse that enable disagreement with respect.

The most effective ways Jews “fought back” a century ago used the framework of democratic norms and institutions. It is the perception of such threats to those institutions that most alarm Jews now. If we are to learn from history, we must understand that safeguarding democracy protects all of us.

Never can I remember so many Jews scrutinizing and grappling with their relationship with America, and with such urgency, as they are today. That is why hundreds of us will gather together at this year’s Feast of Jewish Learning (7 p.m. Saturday, Jan. 26 at Congregation Beth Am in Los Altos, jewishlearningworks.org) to study and discuss the Jewish-American relationship. The theme: “Toward a More Perfect Union: Jews & America.” We hope you will join us.