Cincinnati - Elizabeth Warren offered an impassioned endorsement of Hillary Clinton on Monday morning, symbolically unifying the Democratic Party behind the presumptive nominee and giving voters a rousing preview of what could be a historic joint ticket.Throwing clasped hands high in the air, the two women promised to "go big" and "go bold" to level the playing field for frustrated and angry workers."I'm here today because of her," said Warren, a champion of the party's liberal base, before 2 600 cheering supporters at the historic Cincinnati Museum Centre a Union Terminal. "We're here to fight side by side with Hillary Clinton."The picture-perfect image marked an important moment of party unity after Clinton's long-fought primary against liberal challenger Bernie Sanders, who has not yet endorsed his former rival. And with the Massachusetts senator under consideration to be Clinton's running mate, it may also be a harbinger of the party's future.Warren showed how she could play the role as an attacker-in-chief against Republican Donald Trump, calling him a "small, insecure money-grubber", ''a nasty man" and "goofy".An unprecedented two-woman ticket would electrify the party's liberal wing, boosting enthusiasm for Clinton's campaign as she continues to face high unfavourable ratings.Warren could also help Clinton combat the perception that the multimillionaire former first lady is disconnected from the struggles of working Americans - an image encouraged by Sanders during his campaign.Her arm over Warren's shoulder, Clinton lavished praise on the progressive icon, whom she called a "friend" and a "great leader"."She is considered so terrific, so formidable, because she tells it like it is," she said.Warren returned the compliment: "She just remembers who really needs someone on their side and she gets up and keeps right on fighting for the people who need her the most," she said of Clinton.Frosty relationshipThe two women have never been close, according to aides, who note they didn't overlap in the Senate and worked in different corners of the Obama administration. Clinton served as secretary of state, while Warren helped establish the Consumer Financial Protection Bureau.At times, their relationship has seemed almost frosty. Warren wrote in a 2004 book that as a senator from New York, Clinton "could not afford such a principled position" on legislation that would make it harder for consumers to relieve their debt through bankruptcy laws. She also implied that Clinton was short-tempered and impatient with her staff.There was little of that distance on Monday. They repeatedly hugged, smiled and threw their fists in the air.Together, they slammed Trump, casting him as a small-minded, self-interested billionaire who would destroy the country's economy."Donald Trump is the guy who wants it all for himself," said Warren. "And watch out. Because he will crush you into the dirt to get whatever he wants."She's taken his hits in return: He blasted her as "Pocahontas", a reference to past discussions about her having Native American ancestry."Crooked Hillary is wheeling out one of the least productive senators in the US Senate, goofy Elizabeth Warren, who lied on heritage," Trump tweeted on Monday.Warren's tough assault is valued by Clinton, who aides say particularly appreciates surrogates that don't mince words in their attacks."I do just love to see how she gets under Donald Trump's skin," said Clinton.Warren has been trying to endear herself to Clinton in other ways, too. A few days after a private meeting at Clinton's home, Warren stopped by her campaign headquarters in Brooklyn to deliver a pep talk to staffers. The visit, bragged pleased Clinton staffers, was at Warren's request.Vice presidential search She's currently being vetted by lawyers involved in Clinton's vice presidential search, and they've asked Warren for documents and to complete a questionnaire. The next step: a private interview with Clinton.Other candidates under consideration include Virginia Senator Tim Kaine, a well-liked lawmaker from an important general election battleground state; and Housing and Urban Development Secretary Julian Castro of Texas, a rising star in the Democratic Party.Clinton remains weeks away from making her pick, according to aides.But there was plenty of wishful thinking at her rally."We were really hoping that she would announce that Elizabeth Warren was her vice president," Kristen Woods, 29. "She's amazing. I would love her."