WASHINGTON, United States (AFP) – President Barack Obama launched a full throated defense of open immigration policies Tuesday, hailing them as America’s “oldest tradition” amid a fierce election-fueled argument over the issue.

Hours before Republican candidates were to hold their final presidential debate of the year, one heavily focusing on security and immigration, Obama told 31 newly naturalized Americans that immigration is “who we are.”

“Just about every nation in the world, to some extent, accepts immigrants, but there is something unique about America,” he said in the National Archives rotunda, franked by the US Constitution, Bill of Rights and Declaration of Independence.

“We don’t simply welcome new arrivals, we are born of immigrants, that is who we are, immigration is our origin story,” he said.

“For more than two centuries it’s remained at the core of our national character, it’s our oldest tradition, it’s who we are, its part of what makes us exceptional.”

The campaign to succeed Obama has been marked by tough talk against immigrants and immigration, not least from Republican frontrunner Donald Trump.

The real estate mogul-turned-politician has vowed to ban all Muslims from entering the country and to deport illegal migrants from Latin America.

The debate has taken on a tougher tone amid terror attacks in Paris and California.

One of the husband and wife attackers who killed 14 people in San Bernardino was born in America, the other had arrived on a fiancee visa.

Listing instances of past discrimination against the Japanese, Irish and Italians, Obama said, “On days like today, we need to resolve to never repeat mistakes like that again.”