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Only a few months from now, populist Democratic progressives around the country hoping to elect one of their own to the White House will need to choose between Sen. Bernie Sanders of Vermont and Sen. Elizabeth Warren of Massachusetts.

Do they back the angry Democratic socialist, or the feisty, anti-corporate populist who wants to break up the banks and big tech companies? One says he is trying to lead a revolution. The other calls for dramatic change, often dismissing critics in her own party for regurgitating Republican talking points.

Only one of those hopefuls is now is one of the front-runners for the Democratic presidential nomination. That would be Warren.

Sanders is passionate and intent on becoming the Democratic standard-bearer, and he is still running well in key state and national polls. But it's still very difficult to see the 78-year-old Vermonter becoming the Democratic nominee next year.

This is Sanders' second presidential rodeo, but unlike four years ago, he isn't a quirky novelty this time. He now shares his lane with another top-tier hopeful who echoes his populism. That alternative, Warren, is a woman, is eight years younger than Sanders and is a strong enough speaker to have moved from near obscurity in the race to the top tier.

And unlike Sanders, Warren hasn't embraced socialism.

But the Vermonter's campaign, which has plenty of money, shows no signs of stopping after a relatively brief medical scare. Sanders is a man on a mission, and people like that don't quit easily. He took on Hillary Clinton (and the Democratic National Committee), after all, when nobody else was willing to do so. It's hard to believe that he could be scared out of the presidential race by Warren.

And that is a problem for the Massachusetts Democrat. For as long as Sanders remains in the contest, Warren will have a hard time consolidating support among the party's left.

But Warren has another problem, which follows from her party's desire to beat Trump next year. Many Democrats in the business and financial communities believe that Warren's ultimate agenda is not very different from Sanders' when it comes to raising taxes, sticking it to corporate America, distrusting the free market, adding new entitlements and piling on layers additional debt to pay for new government programs.

Warren's continued embrace of "Medicare for All" has become a substantial problem for her. It's not just the cost of that program. It's the larger message that the government knows better what is good for you than you do. Many in the party prefer Medicare for All Who Want It or Obamacare with a public option, both of which seem more appealing and manageable to pragmatic legislators and voters.

Warren has had plenty of chances to slide to the right slightly, but she never takes them. On health care, all she needed to do to broaden her appeal was to emphasize her willingness to negotiate with others in her party. She could make it clear that while she prefers Medicare for All, she certainly is open to compromise.

But would Warren undermine her own appeal with populist, grassroots progressives who favor dramatic proposals, not piecemeal changes, by giving herself some wiggle room on health insurance? Possibly. But it also might make her seem more reasonable to those worried about her agenda.

Not satisfied to paint herself into a corner on only one issue, Warren has unveiled a K-12 education plan that goes after charter schools. The Washington Post editorial board immediately challenged her, arguing "when it comes to education, Ms. Warren has a plan that seems aimed more at winning the support of the powerful teachers unions than in advancing policies that would help improve student learning."

On one hand, you can say that Warren is simply protecting her left flank, making sure that she doesn't lose true believers to Sanders. The problem is that Warren's positions are less about campaign strategy and more about her views of government and her views of corporate America and the affluent.

Warren may not call herself a Democratic socialist, but her rhetoric and overall approach to issues like health insurance and education puts her far enough left that she would have a hard time appealing to pragmatists and political Independents.

Of course, Warren (or Sanders) would energize the Democratic base and turn out voters who sat on their hands (or voted third party) in 2016, and that could be enough to flip the White House. But Warren's and Sanders' populist progressive positioning would also make it much easier for the GOP to make the 2020 election about them — and socialism — rather than about Trump. And that may be the only way the president can win a second term.

Democratic candidates often move left in the primary but right if and when they make it to the general election, so it's possible that Warren is merely following that well-traveled path. Maybe, if she gets her party's nomination, she will zig and then zag toward the center.

But like Sanders, Warren rarely (really never) conveys the impression that she is prepared to build coalitions, negotiate with friends and foes alike, and eventually forge compromises to enact legislation. Put another way, both Sanders and Warren are as much prisoners of their ideology as Donald Trump is a prisoner of his narcissism.