President Barack Obama delivered a touching and powerful message to immigrants who had just taken the oath of American citizenship during a naturalization ceremony at the National Archives on Tuesday: Immigration—and especially religious freedom for immigrants—is America’s oldest heritage.

The speech also served as a damning rebuke of the calls among Republican presidential candidates to reject refugees seeking to flee the war in Syria or to hold religious tests for them, and especially to Donald Trump’s call for banning Muslims from entering the country.

Going back to before the nation’s founding, Obama described the immigrant experience—and religious freedom for immigrants—as one of the country’s earliest ideals.

“The first refugees were the Pilgrims themselves, fleeing religious persecution, crossing the stormy Atlantic to reach a new world where they might live and pray freely,” he said.

Obama also attempted to portray America’s capacity to accept strangers as one of the country’s greatest strengths, and compared today’s immigrant communities to those of past generations, with a poignant description of the situation facing Syrian refugees. “In the Mexican immigrant today, we see the Catholic immigrant of a century ago,” he said. “In the Syrian seeking refuge today, we should see the Jewish refugee of World War II.”

Finally, he spent a good portion of the speech talking about America’s past failure to live up to those ideals and—at a time when the immigrant- and Muslim-bashing Trump is dominating national polls for the Republican primary—declared we must never betray them again.

“Chinese immigrants faced persecution and vicious stereotypes and were for a time even banned from entering America,” Obama said. “During WWII, German and Italian residents were detained, and in one of the darkest chapters in our history, Japanese immigrants and even Japanese American citizens were forced from their homes and imprisoned in camps.”

“We succumbed to fear. We betrayed not only our fellow Americans, but our deepest values. We betrayed these documents. It’s happened before.”

Clearly nodding to the current moment—days after ISIS-inspired terrorists killed 14 people in San Bernardino, California, and weeks after ISIS-linked terrorists killed 130 in Paris, resulting in a public backlash against Syrian refugees who themselves are fleeing war and/or ISIS—Obama argued that it was in challenging times like these that it was most critical that Americans not fail again to live up to the country’s stated ideals.

“Standing up for each other is what the values enshrined in the documents in this room compels us to do, especially when it’s hard, especially when it’s not convenient,” he said, referring to the nation’s founding documents housed in the Archives where he gave the speech. “That’s when it counts, that’s when it matters. Not when things are easy, but when they’re hard.”

• Barack Obama
• Immigration