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With Democrats facing tough prospects in the midterm elections, will they also have to worry about primary challenges from their left flank?

During his presidential campaign, Sen. Bernie Sanders never quite decided whether his “political revolution” could coexist with the Democratic Party or needed to overthrow it. Now, Sanders is one of the most popular political figures in the country and the activists he galvanized have gone on to start new groups, join old ones, or run electoral campaigns.

The path of Sanders' former staffers reflects the split in his movement, and the some are already galvanizing for the 2018 elections — and setting their sights on their own.

Rep. Keith Ellison, one of Sanders’ most prominent allies, preached unity during his bid for the chairmanship of the Democratic National Committee and is now the party’s deputy chairman.

But the more radical strain, which led hundreds of Sanders delegates to walk out of the Democratic National Convention in protest last summer, is still present on the left and emboldened by the loss of Hillary Clinton and their belief that “Bernie would have won.”

Some are betting that the disaffected left is as or more interested in remaking the Democratic Party as it is in fighting President Donald Trump.

While they’ve yet to prove they are capable of being any kind of a force to be reckoned with, a handful of groups that grew out of the Sanders movement have already begun issuing primary threats against Democratic incumbents.

One called #WeWillReplaceYou has warned specific members of congress it may challenge them. But it promises to use discretion in targeting only those Democrats it feels have strayed from the party.

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Another new group staffed by ex-Sanders aides, Justice Democrats, has less clear plans. While their audacious talk isn't backed up at the moment, they have an innovative model that could be used to run a large slate of candidates on the cheap against possibly dozens of incumbents.

This week, Justice Democrats merged operations with another anti-incumbent group founded by former Sanders aides, Brand New Congress, which started last year.

“The point is we've watched this party over the last decade lose over 1,000 seats, lose a national election to least popular nominee in history, Donald Trump, and now we've seen poll after poll showing the Democratic Party less popular since election day,” Brand New Congress’ Corbin Trent said in an interview. “What we think is the American people are ready for a new direction.”

It's a step farther than previous liberal efforts, which have fielded challenges to establishment favorite Democrats in open races but generally not against elected party members.

If they are able to follow through, the result would likely be a mass of underfunded token candidates, not necessarily serious challengers. But that may still be enough to make their point that members of Congress should not run unopposed in primaries.

Justice Democrats' unusual approach lets anyone nominate potential candidates online. They say they’ve received 8,300 nominations so far and raised $1 million with virtually no marketing. And they claim a large group of volunteers with experience on campaigns who will help coordinate a central political infrastructure to support their entire slate.

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Democratic officials say they’re not too worried about primary challenges in next year’s midterm elections — the Democratic Congressional Campaign Committee declined to comment — but the Tea Party showed in 2009 and 2010 that grassroots opposition movements can sometimes turn on their own party.

The democratic caucuses in both house and senate are likely more liberal than they have ever been, after moderates were culled in the 2010 and 2014 midterm election waves. The so-called Blue Dogs have been largely wiped out and even the red state senators who are Democrats’ top priorities in 2018, are historically fairly progressive for their states.

But for Justice Democrats’ founder, liberal media personality Cenk Uygur, what seems to matter most is inflicting damage on the Democratic Party.

The group’s website features an image of a sledgehammer smashing the “D” logo of the Democratic National Committee and declares “it’s time to rebuild the Democratic Party from scratch.”

Not mentioned hardly anywhere on the site is Trump.

“It is time for them to step aside and let us lead. If you want unity, we’re ready to lead. You get unified on this actual progressive platform,” Uygur said on his popular internet TV show, The Young Turks.

The show's advertising package claims it has 85 million unique monthly views in addition to a core of members who pay $10 a month or more for extra services. That supports a large staff and professional broadcast operation that hosted major guests from Sanders to film director Quentin Tarantino.

Critics say Uygur’s slash-and-burn approach to the Democratic Party is little more than an opportunist attempt to corner the media market for disaffected liberals, and that now he and his ilk are trying to do the same for politics.

There’s not a great track record of similar media entrepreneurs moving into politics. Glenn Beck’s 9/12 Project never amounted to much and former Daily Show host Jon Stewart's massive “Rally for Sanity” in Washington fizzled.