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Republican presidential candidate Donald Trump criticized San Francisco 49ers quarterback Colin Kaepernick Monday, calling Kaepernick's refusal to stand for the national anthem "a terrible thing."

"I think it’s personally not a good thing," Trump told Seattle radio station KIRO when asked about the controversy. "I think it’s a terrible thing, and you know, maybe he should find a country that works better for him, let him try, it’s not gonna happen."

Kaepernick became the subject of national controversy over the weekend when he remained seated on the San Francisco bench during the playing of the "Star-Spangled Banner" prior to Friday night's preseason game against the Green Bay Packers.

While explaning his stance to reporters Sunday, Kaepernick criticized both Trump and Democratic nominee Hillary Clinton.

"You have Hillary who has called black teens or black kids super predators, you have Donald Trump who’s openly racist," Kaepernick said. "We have a presidential candidate who has deleted emails and done things illegally ... That doesn’t make sense to me because if that was any other person you’d be in prison. So, what is this country really standing for?"

The Clinton campaign has not commented on Kaepernick's statements.

White House spokesman Josh Earnest said Monday he was confident President Barack Obama is aware of Kaepernick's actions, but hadn't spoken directly with the president about it.

"In general, what I can say is that I certainly don't share the views that Mr. Kaepernick expressed after the game in explaining his reasoning for his actions, but we surely would all acknowledge and even defend his right to express those views in the settings that he chooses," Earnest said. "That's what he's done, and even as objectionable as we find his perspective, he certainly is entitled to express it."

Kaepernick has characterized his actions as a protest at the state of race relations in America, not as a slight against men and women in the military.

"There's a lot of things that need to change. One specifically? Police brutality," said Kaepernick, who is biracial and whose adoptive parents are white. "There's people being murdered unjustly and not being held accountable. People are being given paid leave for killing people. That's not right. That's not right by anyone's standards."

In a letter to NFL Commissioner Roger Goodell and 49ers CEO Jed York, Martin Halloran, the president of San Francisco's police union, said Kaepernick's statements showed "naiveté" and "total lack of sensitivity" toward police, along with an "incredible lack of knowledge" about officer-involved shootings.

"I only wish Mr. Kaepernick could see the emotional and psychological challenges that our officers face following a fatal encounter," Halloran wrote.

"Some are so affected they never return to the streets. In short, Mr. Kaepernick has embarrassed himself, the 49er organization, and the NFL based on a false narrative and misinformation that lacks any factual basis."

The Associated Press contributed to this report.