MOUNT RUSHMORE NATIONAL MEMORIAL, S.D. (AP) — Speaking to a largely maskless crowd at Mount Rushmore, President Donald Trump said Friday that protesters have waged “a merciless campaign to wipe out our history” amid demonstrations against racial injustice and police brutality.

The sharp rebuke in a holiday address to mark the nation’s independence follows weeks of protests across the nation, sparked by the Memorial Day killing of George Floyd by police in Minneapolis. Some demonstrators have also destroyed or damaged Confederate monuments and statues honoring those who have benefited from slavery.

“This movement is openly attacking the legacies of every person on Mount Rushmore," Trump said, adding that some on the political left hope to “defame our heroes, erase our values, and indoctrinate our children."

His speech, intended to rev up his conservative base, comes as Trump has seen his standing slump over his handling of the pandemic and response to protests and unrest around the country. With four months until the election, Trump’s hopes for a second term — once buoyed by low unemployment and a roaring stock market — seem uncertain.

Amid the headwinds, Trump has sharpened his focus on his most ardent base of supporters as concern grows inside his campaign that his poll numbers in the battleground states that will decide the 2020 election are slipping.

Trump in recent weeks has increasingly lashed out at “left-wing mobs," used a racist epithet to refer to the coronavirus and visited the nation’s southern border to spotlight progress on his 2016 campaign promise to build a U.S.-Mexico border wall.

The event, while not a campaign rally, had the feel of one as the friendly crowd greeted Trump with chants of “Four more years!” and cheered enthusiastically as he and first lady Melania Trump took the stage.

"Those who seek to erase our heritage want Americans to forget our pride and our great dignity, so that we can no longer understand ourselves or America’s destiny,” Trump said.

The event drew thousands of spectators, most of them without masks, even as coronavirus cases spike across the country. The president was set to speak before a big fireworks show, the first to be held at the site in over a decade.

Hours before Trump arrived, protesters blocked a road leading to the monument. Authorities worked to move the demonstrators, mostly Native Americans protesting that South Dakota's Black Hills were taken from the Lakota people against treaty agreements. About 15 protesters were arrested after missing a police-imposed deadline to leave.

Trump was expecting a South Dakota show of support, with the state Republican Party selling T-shirts that feature Trump on the memorial alongside George Washington, Thomas Jefferson, Theodore Roosevelt and Abraham Lincoln. But concern about the coronavirus risk and wildfire danger from the fireworks, along with the Native American groups' protests were also present.

Republican Gov. Kristi Noem, a Trump ally, had said social distancing won't be required during the event and masks will be optional. Event organizers were to provide masks to anyone who wanted them and planned to screen attendees for symptoms of COVID-19.

Noem, in her own remarks, echoed Trump's attacks against his opponents who “are trying to wipe away the lessons of history”

“Make no mistake: This is being done deliberately to discredit America’s founding principles by discrediting the individuals who formed them,” she said.

The small town of Keystone, which lies a couple of miles from the monument, was buzzing with people Friday hoping to catch a glimpse of the fireworks and the president. Many wore pro-Trump T-shirts and hats. Few wore masks.

“This is going to rank up in the top Fourth of Julys that I talk about,” said Mike Stewhr, who brought his family from Nebraska.

Mike Harris of Rapid City, who said he was a Republican, wore a mask and waved an anti-Trump flag. He also was sporting a handgun on each hip. He said he was worried the event would spark a COVID-19 outbreak.

“I think it's a bad example being set by our president and our governor,” Harris said.

Leaders of several Native American tribes in the region raised concerns that the event could lead to virus outbreaks among their members, who they say are particularly vulnerable to COVID-19 because of an underfunded health care system and chronic health conditions.

“The president is putting our tribal members at risk to stage a photo op at one of our most sacred sites,” said Harold Frazier, chairman of the Cheyenne River Sioux Tribe.

Some Native American groups used Trump's visit to protest the Mount Rushmore memorial itself, pointing out that the Black Hills were taken from the Lakota people.

More than 100 protesters, many Lakota, lined the road leading from Keystone to the monument holding signs and playing Lakota music in 95-degree heat. Some held their fists in the air as cars loaded with event attendees passed by. Others held signs that read “Protect SoDak's First People,” “You Are On Stolen Land” and “Dismantle White Supremacy."

“The president needs to open his eyes. We're people, too, and it was our land first,” said Hehakaho Waste, a spiritual elder with the Oglala Sioux tribe.

Several people who once oversaw fire danger at the national memorial have said setting off fireworks over the forest was a bad idea that could lead to a large wildfire. Fireworks were called off after 2009 because a mountain pine beetle infestation increased the fire risks.

Noem pushed to get the fireworks resumed soon after she was elected, and enlisted Trump's help. The president brushed aside fire concerns earlier this year, saying, “What can burn? It's stone.”

Trump has presided over a several large-crowd events — in Tulsa, Okla., and at an Arizona megachurch — even as health officials warn against large gatherings and recommend face masks and social distancing. He plans a July Fourth celebration on the National Mall in Washington despite health concerns from D.C.’s mayor. Trump and Melania Trump plan to host events from the White House South Lawn and from the Ellipse.

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Associated Press writers Jill Colvin and Aamer Madhani in Washington and Todd Richmond in Madison, Wis., contributed to this report.