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Locked hand-in-hand in front of a rapturous Ohio crowd, Hillary Clinton and Elizabeth Warren sealed a powerful alliance Monday that could help unify the Democratic Party and give Donald Trump nightmares.

The Massachusetts senator is on Clinton’s shortlist of potential vice presidential running mates, but campaigning with the presumptive Democratic nominee in Cincinnati, Warren demonstrated she will be a vital ally in any capacity.

The liberal superstar’s imprimatur, which she delivered with gusto and without reservations, will help Clinton win over skeptical Bernie Sanders supporters. Warren’s ability to provoke Trump with cutting attacks is virtually unrivaled in the Democratic Party.

Warren was conspicuously late to endorse Clinton, but seemed to be trying to make up for it with enthusiasm. "Hillary has brains, she has guts, she has thick skin and steady hands. But most of all, she has a good heart. And that’s what America needs. And that’s why I’m with her,” Warren declared, before leading the crowd in chants of “Hill-a-ry! Hill-a-ry!”

She called Trump “a small, insecure money-grubber who fights for no one but himself” and a “thin-skinned bully driven by insecurity and hate.”

"When Donald says he'll make America great, he means greater for rich guys just like Donald Trump,” Warren continued, while “he'll crush you into the dirt.”

Trump sensed the onslaught coming, dismissing the two women in a tweet Monday morning. “Crooked Hillary is wheeling out one of the least productive senators in the U.S. Senate, goofy Elizabeth Warren, who lied on heritage,” he wrote.

Indeed, if Warren hoped to provoke an overheated response from Trump, she was successful. Trump's campaign first released a statement calling Warren a "sellout" for backing Clinton, and not "Pocahontas" -- Trump's controversial go-to jab at Warren, which references a controversy involving her Native American heritage. However, shortly thereafter, Trump called NBC's Hallie Jackson to repeatedly call Warren a "racist" for allegedly inflating her Native American heritage. "We call her Pocahontas for a reason."

But Warren relished the verbal combat, turning the appellation around on Trump -- "You want to see goofy? Look at that hat,” adding, “I could do this all day.”

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The last time Warren and Clinton appeared together, campaigning for a Massachusetts Democrat before the 2014 midterms, it was Clinton who worked hard to align herself with Warren. “I love watching Elizabeth!” Clinton said.

Clinton allies at the time were carefully watching a gathering movement on the left to draft Warren into the 2016 presidential race that Clinton was sure to enter herself. Warren was a potential threat on Clinton’s always-vulnerable left-flank, and Clinton hoped at the time that the senator would offer her some political cover. Warren did not oblige.

“I’m happy to welcome Secretary Clinton back to the commonwealth. We love it,” was all Warren had to say then about the visit from the former secretary of state and first lady.

The two did not even share the stage at the same time, depriving Clinton of a joint photo-op. It was typical of the two women’s sometimes icy, but mostly non-existent relationship over the previous decades.

After Clinton decided to run for the Democratic nomination and Warren did not, the senator remained aloof. She was the only female Democratic senator not to endorse Clinton -- an absence made conspicuous at a Washington fundraiser featuring the other 13 -- keenly aware that her carefully managed support base was split between Sanders and Clinton.

Warren did finally throw her support behind Clinton after she won enough delegates to secure the nomination. On Monday, two weeks after that endorsement, Warren literally joined hands with Clinton and threw her arms above her head in an indisputable display of support and unity.

"I am here today because I'm with her," Warren said, invoking a Clinton campaign slogan.

Warren’s remarks also included plenty of her own biography and first-principles, as if she were introducing herself to a new audience.

It’s unclear what Warren wants from Clinton, and vice versa, but it’s obvious that they both realize they are stronger together -- to paraphrase Clinton’s new slogan -- than apart.

Clinton called Warren "my friend and a great leader," who is "so terrific" and “so formidable" because she "tells it like it is."

Praising Warren on the terms that matter to the senator most, Clinton heaped laurels on the Consumer Finance Protection Bureau, Warren’s brainchild agency. “No one works harder to make sure Wall Street never -- never -- wrecks Main Street again, Clinton added.

The party’s standard-bearer also recognized Warren’s star power, which has in a few short years turned the freshman senator into a potential national political brand. “Some of the best TV since Elizabeth came to the Senate has been on C-SPAN,” Clinton said of Warren’s feisty performances on the Senate floor.

Indeed, Warren’s reception in Ohio at times threatened to upstage Clinton, who has acknowledged that whipping up crowds is not her forte.

While tardy to join, Warren has been a gung-ho surrogate since. She’s visited Clinton’s headquarters in Brooklyn to give staff a pep talk, sent a fundraising email on Clinton’s behalf and delighted Clinton aides by giving Trump one of the best tongue-lashings the Democratic Party has to offer.

As for vice presidential speculation, an all-female ticket is a risk, Clinton aides say, but might be uniquely capable of attacking Trump. The Republican has sky-high unfavorability ratings with women and is currently trailing Clinton by 17 points among women, who make up a majority of voters, according to a new NBC News/Wall street Journal poll.

Republicans have telegraphed an effort to portray Clinton’s embrace of Warren as both pandering to liberals and a sign that Clinton herself is too liberal for the mainstream of the country. “A Clinton-Warren ticket is a nightmare for Brooklyn,” said RNC spokesperson Raj Shah. “The liberal icon exposes all that the left despises in Clinton: close ties to Wall Street, shifting positions on economic issues like trade and Social Security and a dependence on the very big money special interests that Sanders and Warren rail against.”

Winning over restive Sanders supporters remains one of Clinton’s biggest outstanding to-do list items.

Clinton’s brain trust believes Warren is a powerful validator on the left -- though some Sanders supporters called Warren a traitor to the cause when she backed Clinton -- who has the knock-on bonus of making Clinton less reliant on Sanders himself, who has refused to suspend his campaign.

Sanders supporters have already started coming around to Clinton on their own. This month’s NBC News poll shows Clinton with a 12 point net positive rating among the rival’s supporters -- up significantly from a net negative 3 point rating last month.

Still, there’s plenty of room to grow with fewer than half of Sanders supporters saying have a favorable view of Clinton.