There was a time when it wasn't even clear Sen. Elizabeth Warren would endorse Hillary Clinton. That time has passed.

As they took the stage together Monday in Cincinnati, the two politicians locked arms, waved (the old half hug-half wave move) and smiled widely. Warren is among the names buzzed about as a possible pick for vice president on a Clinton ticket. Any questions about chemistry were answered today.

"I'm here today, because I'm with her, yes her," Warren said, alluding to a popular slogan of support for Clinton, to roaring applause from a capacity crowd at the Union Terminal.

Clinton, though, said she wouldn't be "making any news today" when asked whether she would consider Warren for VP.

Warren is a hero of the progressive wing of the Democratic Party, someone who has battled with bank executives and campaigned to reduce student debt. Before Bernie Sanders became a progressive cause, activists on the left had hoped Warren would be the one onstage as the Democratic nominee. They set up "Ready for Warren" and tried to draft her into the presidential primary, but she said no. That energy was transferred to the Sanders campaign, but Clinton hopes with Warren on her side, Sanders holdouts will begin to trickle over to her.

Warren, though, has also been an outspoken critic of the Trans-Pacific Partnership trade deal, an Obama administration agreement Clinton was slow to take a position on during the campaign after calling it the "gold standard" as secretary of state. She ultimately opposed it, as she was being pushed in the primary against Sanders.

The onstage endorsement from Warren was full-throated and enthusiastic. But she also continued her role in recent weeks of attack dog against presumptive Republican nominee Donald Trump, calling him "a nasty man."

Warren went on to say he "will never become president of the United States. Because Hillary Clinton will be the next president of the United States. Hillary Clinton will be the next president of the United States, because she knows what it takes to beat a thin-skinned bully who is driven by greed and hate."

In a statement headlined "Sellout Warren," Trump's campaign said "Senator Elizabeth Warren (D-MA) has become a turncoat for the causes she supposedly supports."

"Warren's campaigning for Clinton stands in stark contrast to the liberal ideals she once practiced," the Trump statement continues. "This sad attempt at pandering to the [Bernie] Sanders wing is another example of a typical political calculation by D.C. insiders."

Trump has dubbed Warren "goofy Elizabeth Warren" and has also repeatedly called her "Pocahontas" because of an issue during her Senate campaign about claiming Native American heritage to get preference in hiring.

Warren seemed to relish going after Trump (incidentally, attacking opponents is often a key role for the vice presidential nominee).

"Donald Trump believes poor, sad, little Wall Street bankers need to be free to defraud anyone they want," said Warren, hitting on one of her favored issues. "Hillary Clinton believes we need strong rules to prevent another financial crisis. Yes, Hillary fights for us. Donald Trump cheats workers and wants to abolish the minimum wage."

With Warren by her side, Clinton said, "I do just love to see how she gets under Donald Trump's thin skin."

It seemed to have worked. Shortly after the speech, Trump called a network TV correspondent to express his displeasure with Warren, calling her "racist" while again using the name Pocahontas.

On a Republican National Committee conference call responding to the Clinton-Warren event, former Massachusetts Sen. Scott Brown, who lost his seat to Warren in 2012, challenged her to take a DNA test to prove her Native American lineage.

At a few points during the speech, Warren led the cheering crowd in chants of "Hillary, Hillary."

On the walls of the hall where they spoke, there were murals depicting moments in history, including workers building skyscrapers, plowing earth and laboring on train tracks. The murals seemed intended to complement Clinton's economic message but also highlight the very types of voters Clinton could struggle the most to reach this election year.

Trump is making a direct appeal to these voters, with his opposition to trade deals and pledge to bring good jobs back to America. He is scheduled to deliver a speech Tuesday in Pennsylvania about trade.

Perhaps trying to get out ahead of this speech, Clinton repeated a little-noticed pledge she made earlier in the campaign.

"I'm going to appoint a trade prosecutor who will report to the president, so we are going to end the abuse of our market," Clinton said.

Clinton pledged to say no to "bad trade deals like the Trans-Pacific Partnership." Trump in his big attack speech last week said Clinton would break her campaign pledge and sign it once she becomes president. Some progressive voters are also skeptical about this pledge.

Another area where some voters, especially supporters of Sanders, are skeptical of Clinton's pledges is Wall Street reform. Warren, who came to prominence advocating on these issues, could give Clinton a dose of credibility there.

Clinton praised Warren, saying that when she is on C-SPAN in Senate hearings pressing bank executives and regulators for answers, "She is speaking for every American who is frustrated and fed up. She is speaking for all of us, and we thank her for that."

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