Presumptive Republican presidential candidate Donald Trump developed a rivalry with Massachusetts Senator Elizabeth Warren, who has been using social media to launch attacks on him. Trump, in a recent interview, referred to Warren as “Pocahontas” over her claim to having Native American heritage in an effort to strike back at her.

Trump rose to popularity by humiliating and belittling his rivals. But, he now has an equal rival in Warren who has no qualms in making similar comments on Trump, particularly on Twitter.

“I’m going to fight my heart out to make sure @realDonaldTrump’s toxic stew of hatred & insecurity never reaches the White House,” Warren tweeted.

Trump took the opportunity of an interview with the New York Time’s Maureen Dowd to get even on the verbal war after Warren described him as a “bully” in one of her posts, the Gawker reported. When Dowd asked Trump whether he was chided by any Republican for his war on Twitter with Warren, he said, “You mean Pocahontas?”

Earlier this week, Trump took to Twitter to fire back at Warren, calling her “Goofy Elizabeth Warren.” Warren said when she saw Trump called her “goofy” she had laughed out loud. “Really? That’s the best you could come up with? Come on. I thought Donald Trump said he was a guy that was good with words,” The Hill quoted her as saying.

In her anti-Trump parade over Twitter, Warren denounced the real estate mogul for inciting violence and praising Putin and said he is “cool with being called an authoritarian.” She added that what happens next will determine the character for all, Republican, Democrat, and Independent.

In another tweet, Warren attacked Trump, calling his policies dangerous and his past record embarrassing, the Times of India reported.

Warren is yet to announce whether she would endorse Hillary Clinton or Bernie Sanders. She also declined to confirm whether she would be Clinton’s running mate if offered.