NEW YORK (AFP) - Donald Trump has dominated the Twitter battle for the White House by insulting and belittling his rivals, but he has found a formidable social media opponent in the fiery senator and potential Democratic vice presidential pick Elizabeth Warren.
While Hillary Clinton prefers to ignore the attacks of her Republican adversary Trump, who blasts the former secretary of state as "crooked," Warren has no qualms about wading into the fray.
The first-term lawmaker from Massachusetts and former Harvard law professor has successfully harnessed social media, in particular Twitter, as a medium for punching out at The Donald.
He parries, or counterpunches with 140-character-or-less blows of his own. She jabs him with bursts of ruthless tweets.
The mud-slinging began in earnest on May 3, when Trump's rivals quit the race and he emerged as the Republican Party's presumptive nominee.
"I'm going to fight my heart out to make sure @realDonaldTrump's toxic stew of hatred & insecurity never reaches the White House," the senator tweeted a few hours later.
Warren is a liberal Democrat with a passionate following. Many supporters have urged her since 2014 to run for president, although she declined to enter this year's contest.
In her anti-Trump Twitter storm she denounced the candidate as one who "incites supporters to violence, praises Putin," says he is "cool with being called an authoritarian," and "puts our servicemembers at risk by cheerleading illegal torture."
"What happens next will test the character for all of us - Republican, Democrat, and Independent," she added.
"It will determine whether we move forward as one nation or splinter at the hands of one man's narcissism and divisiveness."
Trump, whose belligerent bluster has earned him 8.1 million Twitter followers - Warren has a million - has taken to branding his rivals with pithy but obnoxious labels like "Little Marco" Rubio and "Lyin' Ted" Cruz.
He now trains his fire on the Democrats, labelling the White House contenders "Crooked Hillary" and "Crazy Bernie" Sanders.
Recently, he piled criticism on Warren, unveiling a new nickname.
"I hope corrupt Hillary Clinton chooses goofy Elizabeth Warren as her running mate. I will defeat them both," Trump tweeted.
Warren shot back with Trump-like swagger, and the war of words was on.
"'Goofy,' @realDonaldTrump? For a guy with 'the best words' that's a pretty lame nickname. Weak!" she wrote.
Trump then dug up a tiff about Warren's ancestry, repeating conservative accusations that she does not have Native American blood as she has claimed, a controversy that arose during her successful 2012 Senate campaign.
Warren retorted by calling the New York real estate tycoon "a bully who has a single play in his playbook - offensive lies thrown at anyone who calls him out."
Trump "spews insults and lies" in order to avoid honest discussion about issues that are important to Americans, she said.
"Whatever @realDonaldTrump says, we won't shut up. We won't back down. This election is too important, & he won't step foot in White House."
"Goofy Elizabeth Warren is weak and ineffective. Does nothing. All talk, no action - maybe her Native American name?" Trump tweeted back.
After a days-long truce, the attacks resumed before the bemused eyes of millions - in a showdown resembling a reality show more than a presidential campaign.
On Wednesday, Trump struck first, unloading a string of crude tweets including one that assailed Warren's "phony Native American heritage" and said she "didn't have the guts" to run for president.
Warren, who has yet to announce her support of either Clinton or Sanders, and has declined to say whether she would accept an offer to be Clinton's running mate, refused to let up.
"We get it, @realDonaldTrump: When a woman stands up to you, you're going to call her a basket case. Hormonal. Ugly," she responded.
Warren has launched pointed, specific criticism of the billionaire's past business deals, his stance on Wall Street or the minimum wage, and accused him of "scamming students" who enrolled in his now-defunct Trump University.
"@realDonaldTrump: Your policies are dangerous," she tweeted. "Your words are reckless. Your record is embarrassing. And your free ride is over."