WASHINGTON — Beto O'Rourke tried it. Kamala Harris tried it. Cory Booker tried it. And one by one, they all flamed out. Now, Elizabeth Warren is pitching herself as the Democratic candidate who can unify the party's progressive and moderate wings, a play that could lead her down the same bridge to nowhere, unless her message can quickly find some resonance.

The Massachusetts senator has pleaded with voters not to pick a divisive nominee who risks paving the way for President Donald Trump's re-election, telling a devoted crowd of supporters Tuesday in Manchester, New Hampshire, that she was Democrats' "best chance" of marshaling "a unified party" to the voting booths come November.

At the same time, Warren’s also feeling pressure from outside allies to return to her old “fighter” persona. After her unity-centric message flopped in Iowa and New Hampshire — where Warren finished in third and fourth place behind left-wing favorite Bernie Sanders and moderate upstart Pete Buttigieg — one operative supportive of Warren told NBC they hoped the results would be a “kick in the ass” for a campaign that’s been reluctant to stray from its “uniter” message.

The early-state struggles put Warren in a strategic conundrum that she is delicately navigating. She wants to demonstrate her combative streak as a "fighter" without appearing divisive, lest she undercut her closing pitch that she's uniquely suited to unify the party. In recent days she has taken subtle jabs at her main rivals — Sanders and Buttigieg — while reserving her most aggressive attacks for Michael Bloomberg, the billionaire entrepreneur rising in national polls.

The bifurcated message is a gamble that could attract — or alienate — broad swaths of voters.

"The problem that Warren has is all of the Bernie people think she's a neoliberal shill and all of the centrists think she's a raging Maoist," said Sean McElwee, a left-wing organizer and analyst at Data For Progress whose work has been cited by the Warren campaign. "The people who want 'Medicare for All' don't believe she wants it, and the people who don’t want Medicare for All do believe she wants it."

The Democratic establishment has a long memory and remembers Warren’s successful battles against President Barack Obama on Wall Street-friendly personnel and the Trans-Pacific Partnership. On the other end of the spectrum lies a younger left-wing cohort that became aware of Warren in 2016 when she declined to endorse Sanders, and recently grew skeptical when she softened her support for the Medicare for All policy by saying she'd defer that push to her third year in office.

Uniting those factions is Warren’s goal, and she’s learning that it’s easier said than done.

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"We can't have a repeat of 2016. When we roll into the general election with Democrats still mad at Democrats, Democrats still angry, some Democrats staying home — we need to have a party that is united," Warren said on MSNBC's "All In With Chris Hayes," echoing her message to New Hampshire voters on Election Night.

But she has also offered new critiques of her rivals, however subtle. As voters headed to the polls in New Hampshire on Tuesday, she told reporters in Portsmouth that she was “determined to get things done” after being asked if she was more pragmatic than Sanders. “I'm not going to criticize Bernie, you know I haven't. But I've tried to make clear: The approach I use overall, I believe we ought to try to get as much good to as many people as quickly as we can,” she said.

Campaigning in recent days in Virginia and Nevada, Warren has laced into Bloomberg over a report that he faced years of accusations of profane and sexist remarks, and for past comments attributing the 2008 housing crisis to banks ditching the racially discriminatory lending practice of "redlining."

O’Rourke, Harris and Booker all tried to follow a playbook that was successful for Obama — an aspirational message and embrace of progressivism, while steering clear of the most radical ideas on the left in the hope of attracting middle-of-the-road voters. Like Obama, the three endorsed single payer health insurance before backing away from it.

"The other thing that's happened is the moderates are pretty happy with their choices" between Joe Biden, Amy Klobuchar, Buttigieg and Bloomberg, McElwee said. "And the left is pretty happy with its choices. ... Everyone's incentives are to stay in their corner and try to fight it out."

Warren gained traction last year with her message of “big structural change” and promises to fight a corrupt establishment where money talks and ordinary voters’ voices are drowned out. She became a favorite of many liberals and briefly eclipsed Sanders, surging in polls both nationally and in the early states as the candidate “with a plan for that.” But as Sanders rebounded from a heart attack and consolidated the left, Warren rolled out a message of unity mere weeks before voting began.

"One thing we've seen is that above all, voters are looking for authenticity," said Aleigha Cavalier, who was the communications director for the O'Rourke and Deval Patrick campaigns. "They are very, very wary when you change your message midcourse. It might be the right message and it might be really appealing to voters, but they need to believe that you believe it."

And then there's the messenger.

"Women are held to a very, very, very different standard when it comes to authenticity," said Cavalier. "When other candidates in the race do this — and I'm thinking of Pete Buttigieg — he has been given the liberty of changing his message midcourse a number of times in a way that Kamala Harris or Elizabeth Warren have not."

Buttigieg, a little-known mayor of South Bend, Indiana, when he launched his campaign last April, initially spoke in abstract and aspirational terms that intrigued leftists and establishment Democrats. Later in the year, he re-positioned himself as the moderate alternative to Biden and began actively running against ideas like single payer health care and free public college.

Warren’s struggle is rooted in the fact that the two wings of the party aren't fond of each other, each believing deeply that one of their own should win. Moderates say a left-wing nominee would alienate swing voters, assure Trump another four years, and cost Democrats the House. Progressives say the moderates' theory of "electability" has been proven dead wrong by the failed push to elect what they view as milquetoast figures, such as John Kerry in 2004 and Hillary Clinton in 2016.

But Warren allies argue she can marry those two sides in a way that Booker, Harris and O’Rourke could not: By using the “credentials,” as one Democratic operative put it, that she has on the progressive side, plus the good will she’s built up with the more establishment wing.

Her campaign sees it less as a pitch born of being in the middle of two factions, and more as a demonstration of bona fides that can appeal to voters across the aisle. To them, it requires looking no further than Iowa — where Warren won both in liberal Johnson County and (on final alignment) in Sioux County, the state’s most conservative — to see her across-the-party appeal.

Still, so far that appeal has not necessarily translated into votes.

“Warren is somebody who I have respect for, but I have noticed that she slid on her stance on health care. So I'm a little leery," said Dan Declan of Londonderry, New Hampshire, ahead of that state's primary.

Kyle Thurman, another New Hampshire voter, said then that he could imagine himself supporting Warren. “I like her a lot. A lot more than Pete,” he said.

Last week, both of them voted for Sanders.