Democratic presidential front-runner Hillary Clinton has a new partner in her battle against Donald Trump: Senator Elizabeth Warren, who gave a speech today mirroring Clinton's own talking points accusing Trump of profiting from the housing crash of 2008.

Warren, of Massachusetts, has stayed out of the ongoing Democratic primary race between Clinton and Senator Bernie Sanders. She is the only Democratic woman in the Senate who has not endorsed Clinton.

But she recently has become more aggressive in taking on Trump on his favourite medium, Twitter.

Warren's speech, at the Centre for Popular Democracy's annual gala in Washington, struck what are familiar themes for her.

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"Donald Trump was drooling over the idea of a housing meltdown - because it meant he could buy up a bunch more property on the cheap," Warren said.

"What kind of a man does that? Root for people to get thrown out on the street? Root for people to lose their jobs? Root for people to lose their pensions?"

The timing of her remarks today, and their convergence with Clinton's stump message in California the same day, was not entirely a coincidence.

And it may serve a dual purpose for Clinton: helping her begin the general-election battle against Trump, but also beginning the difficult task of unifying the fractured Democratic Party.

Warren enjoys strong support with many of the Democratic constituencies who feel passionately about Sanders. An aide said she is increasingly cognisant of the fact that she is in a unique position to bring those constituencies together and focus the party's energy on defeating Trump.

Among other points, she criticised Trump for proposing a plan that would dismantle Dodd-Frank financial regulations.

"Donald Trump is worried about helping poor little Wall Street?" Warren asked. "Let me find the world's smallest violin to play a sad, sad song."

She added: "Can Donald Trump even name three things that Dodd-Frank does? Seriously, someone ask him."

While campaigning in California, Clinton used Trump's own words to make a similar case: that he cheered on the market crash eight years ago.

"Trump economics is a recipe for lower wages, fewer jobs and more debt," Clinton told a crowd.

"You know what happened in the Great Recession. Donald Trump said when he was talking about the possibility of a housing-market crash before the Great Recession, he said, 'I sort of hope that happens,' " Clinton said. "He actually said he was hoping for the crash that caused hard-working families in California and across the country to lose their homes."

Clinton and over a dozen surrogates and allies hammered the message across the country, showing a level of coordination on message and strategy that amounts to a dry run for the general election.

Elected leaders, including Colorado Governor John Hickenlooper, Congressman Ed Perlmutter, Senator Timothy Kaine, and Congressman Tim Ryan, held calls with local and national reporters to push the message.

"This is Trump's view of the world: When Americans suffer, Trump looks to cash in," Ryan said.

Pro-Clinton group Americans United for Change, the AFL-CIO and other progressive groups rallied outside of Trump's soon-to-be hotel in Washington, District of Columbia, toting anti-Trump signs that repeated - word for word - the message that Ryan delivered on the call.

Trump wasted no time to respond to the attacks.

"I am a businessman, and I have made a lot of money in down markets," he said in a statement distributed to reporters. "In some cases, as much as I've made when markets are good. Frankly, this is the kind of thinking our country needs, understanding how to get a good result out of a very bad and sad situation."

Clinton has for weeks been bogged down in a two-front war against Trump and Sanders. But since Trump essentially secured his party's nomination in April, Democrats have grown increasingly anxious that they are running out of precious time to set the terms of the general election before Trump does.

"We can't normalise Donald Trump - nothing about him is normal," Los Angeles Mayor Eric Garcetti said today.

Democrats have tried out different strategies to take on the presumptive Republican nominee, but on today, Clinton sent a clear signal to her allies that they should focus on a single message: that Trump pursues profit above all else.

The effort was also aimed specifically at voters in battleground states of Ohio, Virginia, Pennsylvania, Florida, New Hampshire, Iowa, Colorado and Nevada.

The Washington Post reported earlier this year that in 2005, Trump ignored growing warnings that the housing market was on shaky ground just before launching his failed mortgage company.

Clinton and her surrogates also called attention to Trump's statements in 2006 and 2007 - in the lead-up to the housing crash in 2008 - saying that if the housing bubble burst, he "would go in and buy like crazy" to make money.

"Now he says he wants to roll back the financial regulations that we have imposed on Wall Street to let them run wild again," Clinton said.

She noted that Trump has "experience with bankruptcy" and questioned how he lost money in the casino business.

"He's bankrupted companies," Clinton said. "I don't know if that's one of the qualifications of running for president, but I kind of doubt it."