LAVEEN VILLAGE, Ariz. — President Joe Biden on Friday formally apologized to Native Americans for the “sin” of a government-run boarding school system that for decades forcibly separated children from their parents, calling it a “blot on American history” in his first presidential visit to Indian Country.

“It’s a sin on our soul,” said Biden, his voice full of anger and emotion. “Quite frankly, there’s no excuse that this apology took 50 years to make.”

It was a moment of both contrition and frustration as the president sought to recognize one of the “most horrific chapters” in the national story. Biden spoke of the abuses and deaths of Native children that resulted from the federal government’s policies, noting that “while darkness can hide much, it erases nothing” and that great nations “must know the good, the bad, the truth of who we are.”

“I formally apologize as president of United States of America for what we did,” Biden said. The government’s removal of children from their Native American community for boarding schools “will always be a significant mark of shame, a blot on American history. For too long, this all happened with virtually no public attention, not written about in our history books, not taught in our schools.”

Democrats hope Biden’s visit to the Gila River Indian Community’s land on the outskirts of Phoenix’s metro area will also provide a boost to Vice President Kamala Harris’ turnout effort in a key battleground state. The moment gave Biden a fuller chance to spotlight his and Harris’ support for tribal nations, a group that historically has favored Democrats, in a state he won just by 10,000 votes in 2020.

The race between Harris and former President Donald Trump is expected to be similarly close, and both campaigns are doing whatever they can to improve turnout among bedrock supporters.

“The race is now a turnout grab,” said Mike O’Neil, a non-partisan pollster based in Arizona. “The trendlines throughout have been remarkably steady. The question is which candidate is going to be able to turn out their voters in a race that seems to be destined to be decided by narrow margins.”

Biden has been used sparingly on the campaign trail by Harris and other Democrats since he ended his reelection campaign in July.

But analysts say Biden could help Harris in her appeal with Native American voters.

In 2020, there was a surge in voter turnout on some tribal land in Arizona as Biden beat Trump and became the first Democratic presidential candidate to win the state since Bill Clinton in 1996.

Biden, whose presidency is winding down, had promised tribal leaders nearly two years ago that he would visit Indian Country.

For decades, federal boarding schools were used to assimilate children into white society, according to the White House. Not everyone saw the apology as sufficient.

“An apology is a nice start, but it is not a true reckoning, nor is it a sufficient remedy for the long history of colonial violence,” said Chase Iron Eyes, director of the Lakota People’s Law Project and Sacred Defense Fund.

At least 973 Native American children died in the U.S. government’s abusive boarding school system over a 150-year period that ended in 1969, according to an Interior Department investigation that called for a U.S. government apology.

At least 18,000 children, some as young as 4, were taken from their parents and forced to attend schools that sought to assimilate them.

“President Biden deserves credit for finally putting attention on the issue and other issues impacting the community,” said Ramona Charette Klein, 77, a boarding school survivor and an enrolled member of the Turtle Mountain Band of Chippewa. “I do think that will reflect well on Vice President Harris, and I hope this momentum will continue.”

Democrats have stepped up outreach to Native American communities.

Both Harris and her running mate, Minnesota Gov. Tim Walz, met with tribal leaders in Arizona and Nevada this month.