Joining Hillary Clinton for a campaign rally in Ohio, Sen. Elizabeth Warren of Massachusetts called the presumptive Democratic presidential nominee a fighter who "has never backed down."
The two women joined hands and waved to a cheering crowd in Cincinnati on Monday during their first joint appearance.
"I'm here today because I'm with her," said Warren, a leader of the party's progressives who is being considered as a possible running mate for Clinton. She said Democrats should "work our hearts out" to make Clinton president.
Warren offered yet another harsh critique of likely Republican nominee Donald Trump, calling the billionaire businessman "a small, insecure money grubber" and "a nasty man who will never become president of the United States."
She said Clinton "knows what it takes to beat a thin-skinned bully who is driven by greed and hate."
"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 most," Warren said.
At one point Warren led the crowd in changing "Hillary, Hillary."
Clinton, for her part, offered effusive praise of the Massachusetts senator. She said Warren defends hard-working Americans and works to ensure Wall Street "never wrecks" Main Street again.
The Democratic presidential candidate said she loves how Warren "gets under Donald Trump's thin skin," a nod to Warren's recent role as one of Trump's harshest critics.
Clinton said Trump "proves every day he's not in it for the American people, he's in it only for himself."
The event spurred a back-and-forth over goofiness on Monday.
"Crooked Hillary is wheeling out one of the least productive senators in the U.S. Senate, goofy Elizabeth Warren, who lied on heritage," Trump tweeted.
Warren, in turn, called Trump's hat "goofy."
In recent weeks, Clinton and Warren have formed a tight electoral alliance — one that could grow even closer should Clinton pick Warren as her running mate. Warren is 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 two women, however, have never been close, according to aides. They didn't overlap in the Senate and worked in different corners of the Obama administration, with Clinton serving 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.
But with the primary season over and Vermont Sen. Bernie Sanders fading from the spotlight, Warren has mobilized behind Clinton, lending her presidential bid a powerful boost of liberal credibility.
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, said Clinton staffers, was at Warren's request.
"Warren, with everything she's done these past few weeks, has made it really hard for her not to be looked at," said Mary Ann Marsh, a Boston-based Democratic strategist. "She has demographic pull. She's got the economic portfolio and no one's taken on Trump better."
For Clinton, the visit to swing state Ohio offers an important opportunity to win back some of the liberal and younger voters she lost to Sanders in the primary. Though Sanders said on Friday that he'd vote for Clinton, he's shied away from offering a full-throated endorsement or urging his supporters to back her.
"It sends a clear signal to progressive voters that it's time for them to put the past in the past and elect Clinton," said Geoff Garin, a pollster at Priorities USA, a super PAC backing Clinton's bid. "Sen. Warren carries an enormous amount of credibility with exactly the same kind of people who were avidly supportive of Sanders in the primary."