Washington: Hillary Clinton unleashed one of her most potent surrogates Monday to wallop rival Donald Trump, with Senator Elizabeth Warren warning Americans that the provocative billionaire will "crush you into the dirt" if he is elected president.

With the White House battle raging months before Americans vote in November, Democrat Clinton campaigned for the first time alongside the liberal icon, who came out swinging against Republican Trump in a likely preview of her attack-dog role in the campaign.

The Massachusetts senator introduced Clinton at a raucous rally in Cincinnati in swing state Ohio, painting Trump as a selfish, "thin-skinned bully."

"You want to see goofy? Look at him in that hat," Warren said, referring to Trump''s propensity to deliver campaign speeches wearing a cap with his logo, "Make America Great Again" -- and his use of nickname "Goofy Elizabeth Warren" for the senator.

"When Donald Trump says he''ll make America great, he means make it even greater for rich guys just like Donald Trump," she said.

"And watch out, because he will crush you into the dirt to get whatever he wants," she thundered. "That''s who he is."

Warren, 67, is often discussed as a possible Clinton vice presidential pick, and Monday''s imagery -- similar blue suit jackets, arms raised in unison -- did little to dispel such speculation.

Warren''s support for working-class Americans has made her a favorite with liberals, and she appeared to relish her opportunity to lay into Trump on the national stage.

"You know I could do this all day," she said.

Like Clinton, Warren blasted Trump''s very public self-congratulation about predicting the British people''s vote last week to leave the European Union.

"He said, hey, it might bring more rich people to his new golf course," she said, even as the crisis caused US retirement accounts to lose billions of dollars in value.

"What kind of a man roots for people to lose their jobs, to lose their homes, to lose their life''s savings?" Warren asked. "I''ll tell you what kind of a man. A small, insecure money-grubber who fights for no one but himself."

- Under Trump''s skin -

Trump had praised the so-called "Brexit" decision during his Friday trip to Scotland where he re-inaugurated one of his golf properties.

Warren stressed that while Trump fuels fear and negativity, Clinton is the race''s optimist.

"Hillary has brains, she has guts, she has thick skin and steady hands, but most of all, she has a good heart," Warren said. "That''s what America needs, and that''s why I''m with her. Are you with her?" she said to a loud roar.

Clinton, 68, who has ratcheted up her Trump criticism in recent weeks, praised Warren for knocking the real estate tycoon off balance.

"I do just love to see how she gets under Donald Trump''s thin skin," Clinton said with a smile, as the crowd cheered.

"She exposes him for what he is: temperamentally unfit and totally unqualified to be president of the United States."

Warren, who claims some Native American blood, has engaged in a war of words with Trump in recent weeks, and the longtime consumer protection advocate has signaled she is all too willing to go head to head with The Donald.

Trump has attacked Warren over her heritage, derisively calling her "Pocahontas," while he and surrogates have accused Warren of lying about her ancestry in order to get plum teaching jobs at Harvard.

"She''s not Native American," Scott Brown, who lost his US Senate seat to Warren in 2012, argued on a conference call.

"I found her audition to be very uncomfortable," he said of Warren''s appearance with Clinton despite their clear differences on some issues.

The Trump campaign blasted Warren as a "turncoat" for backing Clinton despite their differences on the Iraq war -- Clinton voted for it in 2002, Warren was opposed -- and Wall Street, which Warren has worked tirelessly to rein in.

"This sad attempt at pandering to the Sanders wing is another example of a typical political calculation by (Washington) D.C. insiders," Trump''s campaign said in a statement, referring to Clinton''s liberal Democratic nomination rival Bernie Sanders.

AFP