At their first rally together, Democratic presidential candidate Hillary Clinton spoke about Sen. Elizabeth Warren (D-Mass.), as a champion of working-class families. Clinton is vetting Warren as a potential vice-presidential nominee. (Reuters)

At their first rally together, Democratic presidential candidate Hillary Clinton spoke about Sen. Elizabeth Warren (D-Mass.), as a champion of working-class families. Clinton is vetting Warren as a potential vice-presidential nominee. (Reuters)

If there were any doubt that Hillary Clinton and Elizabeth Warren are the “it” couple of the moment in Democratic politics, it was silenced here Monday when they took the stage together for the first time.

The two nerdy wonks and feisty grandmothers, who built rival power centers on the political left but this spring gradually became allies, together electrified a crowd of thousands by locking their arms, punching the air and excoriating Donald Trump.

Clinton may be the one running for president, but Warren, her new surrogate and possibly future running mate, stole the show with her eviscerating takedown of Trump — and her enthusiastic endorsement of Clinton.

The senator from Massachusetts labeled the presumptive Republican presidential nominee “a small, insecure money-grubber,” “a thin-skinned bully” and “a nasty man” who would “crush you into the dirt to get whatever he wants.” Then she critiqued his fashion choices.

“Donald Trump says he will ‘make America great again.’ It is right there — it’s stamped on the front of his goofy hat,” Warren said, knowingly using the same adjective Trump uses to taunt her on Twitter. “You want to see goofy? Look at him in that hat.”

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Clinton smiled, chuckled, nodded and clapped — and by the time she swapped places with Warren at the microphone, she didn’t bother trying to emulate the senator with raw jabs. Rather, she congratulated her.

“I do just love to see how she gets under Donald Trump’s thin skin,” Clinton said, laughing.

As if on cue, Trump quickly responded to Warren, telling NBC News that she is “a total fraud,” “very racist” and “easy” to compete against. He again called her “Pocahontas,” a slur alluding to controversy about Warren’s claim of partial Native American heritage.

[Trump’s ‘Pocahontas’ attack leaves fellow Republicans squirming (again)]

Monday’s joint appearance at the historic Cincinnati Union Terminal — a grand Art Deco-style train station-turned-museum, adorned with colorful murals depicting steel and railroad workers, farmers and pioneers — amounted to a vice-presidential tryout for Warren, who is being formally vetted for the job by Clinton’s lawyers and advisers.

The late-morning rally was a long time in the making, as Warren became one of the last Democratic leaders — and the very last female Democratic senator — to endorse Clinton; she did so only after Clinton’s victory in California four weeks ago against Sen. Bernie Sanders of Vermont all but ended primary season.

Clinton and Warren are not natural partners. Warren has publicly assailed the centrist domestic policies of Bill Clinton’s presidency and has portrayed Hillary Clinton as too close to Wall Street.

Sen. Elizabeth Warren (D-Mass.), center, watches as presumptive Democratic presidential nominee Hillary Clinton addresses a rally Monday in Cincinnati. (Melina Mara/The Washington Post)

Trump’s campaign issued a statement calling Warren “a turncoat for the causes she supposedly supports,” highlighting their differences on issues such as trade and Clinton’s coziness with the financial industry that Warren fights against.

But there was no visible tension between Clinton and Warren as they shared the stage for 47 minutes. The two women, born 20 months apart, apparently have bonded over being grandmothers. Clinton warmly recalled a recent phone conversation with Warren in which Warren told her she was on her way to buy her granddaughter “some sparkly shoes.”

[Hillary Clinton has a new weapon against Trump: Elizabeth Warren]

The coming-together extends to the policy realm as well. As Clinton outlined liberal planks of her domestic agenda — college affordability, Wall Street regulations, infrastructure spending — Warren held onto Clinton’s every line. She stood over Clinton’s shoulder mouthing the word “yes” or punching her fist in the air or throwing her hands up.

In her remarks, Warren testified to Clinton’s progressive credentials and cast her as a fearless fighter for working people.

“Hillary has brains, she has guts, she has thick skin and steady hands, but most of all, she has a good heart, and that is what America needs and that is why I’m with her,” Warren said.

A ticket led by two women would be a historic first; someone in the crowd stoked the possibility by holding up a large sign that read “Girl Power.” Warren has some big-name boosters, including Senate Minority Leader Harry M. Reid (D-Nev.), but many senior Democrats predict Clinton is more likely to opt for a politically safer choice in a running mate, such as Sen. Timothy M. Kaine of Virginia.

“They’re both good on the campaign trail — very good — but I’m not sure the country can take two women. I’m just not sure,” said Rep. John Lewis (D-Ga.), a leader of the civil rights movement.

Clinton fans at Monday’s rally echoed that concern.

“She’s fabulous,” Lana Gallop, 47, a travel agent, said of Warren. “But I don’t think Hillary will pick her. I really think America is not ready for two women on the ticket. I’m ready — hell, yeah, I am — but I don’t think the country is there.”

Clinton has campaigned alongside several possible running mates, including Housing Secretary Julián Castro and Sen. Sherrod Brown of Ohio. But her rally with Warren had a different feel. It easily was one of the most electric events of Clinton’s campaign.

[Clinton is vetting three for vice president — and is still studying a longer list]

When Warren said Clinton “knows what it takes to beat a thin-skinned bully” and “doesn’t run to Twitter to call her opponents ‘fat pigs’ or ‘dummies,’ ” the crowd erupted with chants of “Hill-a-ry! Hill-a-ry! Hill-a-ry!”

At that point, one of Clinton’s advisers who had been carefully watching Warren’s performance whispered to a reporter, “We’ve got to do something about this enthusiasm gap” — a sardonic reference to the media narrative that Clinton’s campaign lacks energy.

In the crowd, Jamie Stocker, 25, a teacher, said, “When they walked out on stage, it was such a heavy moment. I had goose bumps. I was almost going to cry. It’s history, right here.”

Watching on television, Democratic strategist Mary Anne Marsh said Clinton and Warren were “the most effective one-two punch there is against Donald Trump. It was like spontaneous combustion.”

Marsh, who for months now has advocated a Clinton-Warren ticket, said it was clear that both women were primed for the fall campaign. “That performance today, you can’t teach that,” she said. “You can’t rehearse that. That was both of them at their best, in their own way.”

Warren appeared to relish her role as Trump attack dog. About 15 minutes into her remarks, she said, “You know, I could do this all day,” before pleading with the audience to let her get in one more swipe — this one about Trump’s incendiary commentary about blacks, Muslims, Latinos and women. The crowd ate it up.

“She makes me more excited about Hillary,” Pamela Rees, 54, who owns a manufacturing company, said about Warren. “Elizabeth is an inherently more vivacious campaigner. Hillary is presidential, and that’s different.”

Watching Warren go after Trump, she added, “You’ve got to love that. She doesn’t mince words and she gives it back to him, punch for punch.”