Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE on Monday said that calling Sen. Elizabeth Warren Elizabeth WarrenBiden's fiscal program: What is the likely market impact? Warren, Schumer introduce plan for next president to cancel ,000 in student debt The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon MORE (D-Mass.) “Pocahontas” is only demeaning to the renowned Native American.

“I do regret calling her Pocahontas, because I think it’s a tremendous insult to Pocahontas,” he said on Fox News’s “The O’Reilly Factor" Monday night. "So, to Pocahontas, I would like to apologize to you.”

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Anchor Bill O’Reilly also asked Trump, the GOP’s presumptive presidential nominee, whether he would consider Warren for “ambassador to Tonga.”

“No, she wouldn’t be my first choice,” Trump responded. "You know, she’s been a very, very poor senator. You know the funny thing about Elizabeth Warren, she’s been a lousy senator. She’s done a terrible job.”

Trump has repeatedly dubbed Warren “Pocahontas,” reviving past controversy over the senator’s claims of Native American heritage.

Warren has frequently sparred with Trump in recent weeks, attacking the billionaire’s background and disparaging remarks he has made about women.

Warren last week visited Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE’s presidential campaign headquarters in New York City, fueling speculation she may be a vice presidential pick.

Clinton, the presumptive Democratic presidential nominee, was not present during Warren’s appearance.

Warren reportedly discussed protecting ObamaCare and the Dodd-Frank financial reform law during her visit.

Warren’s stop followed her endorsement of Clinton earlier in June after months of neutrality in the Democratic presidential primary.

“I’m ready to get in this fight and work my heart out for Hillary Clinton to become the next president of the United States and make sure Donald Trump never gets anywhere near the White House,” she said on MSNBC on June 9.

Clinton leads Trump by 6 points nationwide, according to the latest RealClearPolitics average of polls.

Trump on Monday said he would close the gap in voter popularity separating him from Clinton before this November.

“I think it’s very close,” he said of the general presidential election. "It’s fairly early to have polling. I think we haven’t even gotten started yet. But I think it’s pretty even from what I’m seeing."