GOP presidential front-runner Donald TrumpDonald TrumpNew York Times to increase spending on Trump coverage despite budget cuts Greens expand ad campaign against Trump EPA pick The Hill's 12:30 Report MORE on Monday called Sen. Elizabeth WarrenElizabeth WarrenThe Hill's 12:30 Report Ethics chief thrust into spotlight by Trump battle Warren blasts Trump for John Lewis criticism MORE (D-Mass.) an “Indian,” mocking her for an old claim of Native-American ancestry.

Earlier in the day, Warren went on a Twitter rant against Trump, calling him a "loser" and a "serious threat" to the United States.

“You mean the Indian?” Trump asked when a reporter inquired about the senator's comments during a press conference in Washington, D.C. “Who’s that? The Indian?”

Trump accused Warren of inflaming tensions between everyday Americans by attacking the legitimacy of his White House run.

“The problem with this country right now is it’s so divided,” he said. "People like Elizabeth Warren really have to get their act together because it’s going to stay divided."

“That includes Hillary,” Trump continued. "And that probably includes me."

Warren met with controversy during her 2012 Senate campaign when reports emerged that Harvard Law School once touted her alleged Cherokee and Delaware ancestors as proof of its faculty’s diversity.