Hillary Clinton is going after Bernie Sanders harder than ever before — and it could hurt Democrats in 2020

Hillary Clinton has taken off the "straitjacket" she says she was forced into during the 2016 Democratic primary.

In her new campaign memoir, the former presidential candidate wasn't exactly subtle about her disapproval of Sen. Bernie Sanders' campaign against her for the Democratic presidential nomination, writing that Sanders, a Vermont independent, caused her "lasting damage," deepened divisions among progressives, and "pav[ed] the way for then candidate Donald Trump's 'Crooked Hillary' campaign."

While many, including Sanders, dismissed Clinton's criticism as an irritating re-hashing of a now-irrelevant battle, the divisions between Clinton's centrist wing of the Democratic Party and Sanders' more progressive (or more populist) supporters couldhave implications for Democrats in the 2018 midterms and even the 2020 presidential election.

'Purity tests'

The day after Clinton released her book, Sanders unveiled his much-anticipated single-payer healthcare plan. Short on details and ambitious in its vision, the proposal won the endorsement of 15 top Democrats, many of them likely 2020 presidential candidates.

But other party leaders, including Senate Minority Leader Chuck Schumer and House Minority Leader Nancy Pelosi, distanced themselves from the plan.

"We want to move the issue forward," Schumer said, adding that "there are are many different bills out there," including "many good ones" that he and other Democrats are examining.

Pelosi warned that support for a single-payer system shouldn't become a "litmus test" for Democrats.

In an interview on the liberal podcast "Pod Save America," Clinton said that while she supports the proposal as a "political statement," she doubts it's much more than a pipe dream at this point.

She also criticized the plan's lack of particulars in an interview with Vox.

"I don't know what the particulars are," Clinton told Vox. "As you might remember, during the campaign he introduced a single-payer bill every year he was in Congress — and when somebody finally read it, he couldn't explain it and couldn't really tell people how much it was going to cost."

14 PHOTOS
Bernie Sanders' 'Medicare for All'
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Bernie Sanders' 'Medicare for All'
Senator Bernie Sanders, an independent from Vermont, speaks during a health care bill news conference on Capitol Hill in Washington, D.C., U.S., on Wednesday, Sept. 13, 2017. Fifteen Senate Democrats are flirting with a single-payer health-care system that would expand Medicare coverage to all Americans, marking a shift within the party on what was once viewed as a politically treacherous issue that attracted little support from lawmakers. Photographer: Andrew Harrer/Bloomberg via Getty Images
Senator Elizabeth Warren, a Democrat from Massachusetts, left, listens as Senator Bernie Sanders, an independent from Vermont, speaks during a health care bill news conference on Capitol Hill in Washington, D.C., U.S., on Wednesday, Sept. 13, 2017. Fifteen Senate Democrats are flirting with a single-payer health-care system that would expand Medicare coverage to all Americans, marking a shift within the party on what was once viewed as a politically treacherous issue that attracted little support from lawmakers. Photographer: Andrew Harrer/Bloomberg via Getty Images
An attendee wears a Senator Bernie Sanders, an independent from Vermont, campaign t-shirt while holding a sign before the start of a health care bill news conference on Capitol Hill in Washington, D.C., U.S., on Wednesday, Sept. 13, 2017. Fifteen Senate Democrats are flirting with a single-payer health-care system that would expand Medicare coverage to all Americans, marking a shift within the party on what was once viewed as a politically treacherous issue that attracted little support from lawmakers. Photographer: Andrew Harrer/Bloomberg via Getty Images
Senator Kamala Harris, a Democrat from California, speaks as Senator Bernie Sanders, an independent from Vermont, left, listens during a health care bill news conference on Capitol Hill in Washington, D.C., U.S., on Wednesday, Sept. 13, 2017. Fifteen Senate Democrats are flirting with a single-payer health-care system that would expand Medicare coverage to all Americans, marking a shift within the party on what was once viewed as a politically treacherous issue that attracted little support from lawmakers. Photographer: Andrew Harrer/Bloomberg via Getty Images
Senator Bernie Sanders (I-VT) speaks during an event to introduce the "Medicare for All Act of 2017" on Capitol Hill in Washington, U.S., September 13, 2017. REUTERS/Yuri Gripas
A member of the audience holds up a placard as US Senator Bernie Sanders, Independent from Vermont, discusses Medicare for All legislation on Capitol Hill in Washington, DC, on September 13, 2017. The former US presidential hopeful introduced a plan for government-sponsored universal health care, a notion long shunned in America that has newly gained traction among rising-star Democrats. / AFP PHOTO / JIM WATSON (Photo credit should read JIM WATSON/AFP/Getty Images)
UNITED STATES - SEPTEMBER 13: Sen. Cory Booker, D-N.J., speaks during Sen. Bernie Sanders' event to introduce the Medicare for All Act of 2017 on Wednesday, Sept. 13, 2017. (Photo By Bill Clark/CQ Roll Call)
Senator Bernie Sanders (I-VT) speaks during an event to introduce the "Medicare for All Act of 2017" on Capitol Hill in Washington, U.S., September 13, 2017. REUTERS/Yuri Gripas
Senator Bernie Sanders (I-VT) speaks during an event to introduce the "Medicare for All Act of 2017" on Capitol Hill in Washington, U.S., September 13, 2017. REUTERS/Yuri Gripas
Members of the audience greet Senator Bernie Sanders (I-VT) during an event to introduce the "Medicare for All Act of 2017" on Capitol Hill in Washington, U.S., September 13, 2017. REUTERS/Yuri Gripas
Attendees hold signs while waiting for a health care bill news conference to begin on Capitol Hill in Washington, D.C., U.S., on Wednesday, Sept. 13, 2017. Fifteen Senate Democrats are flirting with a single-payer health-care system that would expand Medicare coverage to all Americans, marking a shift within the party on what was once viewed as a politically treacherous issue that attracted little support from lawmakers. Photographer: Andrew Harrer/Bloomberg via Getty Images
UNITED STATES - SEPTEMBER 13: The audience waves signs as Sen. Bernie Sanders, I-Vt., speaks during his event to introduce the Medicare for All Act of 2017 on Wednesday, Sept. 13, 2017. (Photo By Bill Clark/CQ Roll Call)
WASHINGTON, DC - SEPTEMBER 13: Supporters watch as U.S. Sen. Bernie Sanders (I-VT) (R) arrives at an event on health care September 13, 2017 on Capitol Hill in Washington, DC. Sen. Sanders held an event to introduce the Medicare for All Act of 2017. (Photo by Alex Wong/Getty Images)
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Democratic strategist Rodell Mollineau, a co-founder of the consulting firm Rokk Solutions, echoed this skepticism.

"I believe in single-payer," he said. "I think there's a big difference between saying you support single-payer and figuring out a way to get the votes and an economic plan in order to get it passed and to pay for it."

Clinton raised the issue of ideological "purity" in her book, arguing that Sanders unfairly narrowed the progressive platform.

"It was beyond frustrating that Bernie acted as if he had a monopoly on political purity and that he had set himself up as the sole arbiter of what it meant to be progressive," she wrote, adding that Sanders simultaneously gave "short shrift to important issues such as immigration, reproductive rights, racial justice, and gun safety."

Mollineau warns that ideological tests could prove just as dangerous for more centrist candidates in 2020.

"When I hear or read that there's some folks who think that someone like a Kamala Harris might not be progressive enough to be our nominee in 2020 — now regardless of whether you support her or not, that's a ludicrous statement and it's a horrible way of applying a purity test," he said.

Steve Schale, a Florida-based Democratic strategist and former adviser to President Barack Obama in the state, says that ideological debates among progressives are not what the party needs right now.

"We're not going to win elections trying to make sure that we have 100% loyalty among 35 or 40% of the electorate, which is what Democrats are," Schale said. "We've got to have a conversation about how we grow the appeal."

Unity among liberals is important, Schale argues, but not nearly as critical as opening the party back up to those independents or one-time Democratic voters who, for a myriad of reasons, abandoned Clinton.

"It's easy to scapegoat the base, or to scapegoat Sanders voters," he said. "But the reality is that [Clinton] lost because the places Barack Obama was much more competitive in in 2008 and 2012 ... she just got torched in."

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People who might run against Trump in 2020
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People who might run against Trump in 2020

Former Vice President Joe Biden

(Photo by Patrick T. Fallon/Bloomberg via Getty Images)

Sen. Bernie Sanders (I-Vt.)

(Photo by Scott Eisen/Getty Images)

Sen. Elizabeth Warren (D-Mass.)

(Photo by Craig F. Walker/The Boston Globe via Getty Images)

Sen. Kamala Davis (D-Calif.)

(Photo By Bill Clark/CQ Roll Call)

Sen. Chris Murphy (D-Conn.)

(Photo by Zach Gibson/Getty Images)

Sen. Amy Klobuchar (D-Minn.)

(Photo by Drew Angerer/Getty Images)

Facebook CEO and founder Mark Zuckerberg

(Photo by David Paul Morris/Bloomberg via Getty Images)

Sen. Cory Booker (D-N.J.)

(Photo by Jason LaVeris/FilmMagic)

Sen. Kirsten Gillibrand (D-N.Y.)

(Photo by: Lloyd Bishop/NBC/NBCU Photo Bank via Getty Images)

Colorado Gov. John Hickenlooper

(Photo By Bill Clark/CQ Roll Call)

New York Gov. Andrew Cuomo

(Photo credit MENAHEM KAHANA/AFP/Getty Images)

Former Maryland Gov. Martin O'Malley

(Photo credit NICHOLAS KAMM/AFP/Getty Images)

Former Housing and Urban Development Secretary Julian Castro

(Photo by Pete Marovich/Bloomberg via Getty Images)

Sen. Tim Kaine (D-Va.)

(Photo by Daniel Acker/Bloomberg via Getty Images)

Sen. Al Franken (D-Minn.)

(Photo by Zach Gibson/Getty Images)

Sen. Al Franken (D-Minn.)

(Photo credit ZACH GIBSON/AFP/Getty Images)

Former Massachusetts Gov. Deval Patrick

(Photo by Suzanne Kreiter/The Boston Globe via Getty Images)

New York City Mayor Bill de Blasio

(Photo by James Keivom/NY Daily News via Getty Images)

Dallas Mavericks owner Mark Cuban

(Photo by Andrew Harrer/Bloomberg via Getty Images)

Environmental activist Tom Steyer

(Photo by David Paul Morris/Bloomberg via Getty Images)

Democratic National Committee Chairman Tom Perez

(Photo by Taylor Hill/FilmMagic)

Minnesota Gov. Mark Dayton 

(Photo by Stephen Maturen/Getty Images)

Virginia Gov. Terry McAuliffe

(Photo by Drew Angerer/Getty Images)

California Lt. Gov. Gavin Newsom

(Photo by Yichuan Cao/NurPhoto via Getty Images)

Facebook COO Sheryl Sandberg

(Photo credit FABRICE COFFRINI/AFP/Getty Images)

Starbucks CEO Howard Schultz

(Photo by Stephen Brashear/Getty Images)

Former first lady Michelle Obama

(Photo by Gerardo Mora/Getty Images)

Dwayne "The Rock" Johnson

(Photo by Donna Ward/Getty Images)

Rep. Tulsi Gabbard (D-Hawaii)

(Photo credit TIMOTHY A. CLARY/AFP/Getty Images)

Rep. Keith Ellison (D-Minn.)

(Photo by Alex Wong/Getty Images)

Rep. Sean Patrick Maloney (D-N.Y)

(Photo By Tom Williams/CQ Roll Call)

California Gov. Jerry Brown

(Photo by Tiffany Rose/Getty Images for Caruso )

Media mogul Oprah Winfrey

(Photo by Moeletsi Mabe/Sunday Times/Gallo Images/Getty Images)

Former Sen. Russ Feingold (D-Wis.)

(Photo By Tom Williams/CQ Roll Call)

Former Vermont Gov. Howard Dean

(Marcus Yam / Los Angeles Times)

Former Vice President Al Gore

(Photo credit DAVID MCNEW/AFP/Getty Images)

Sen. Mark Warner (D-Va.)

(Photo by Katherine Frey/The Washington Post via Getty Images)

Former Sen. Jim Webb (D-Va.)

(Photo by Andrew Harrer/Bloomberg via Getty Images)

Los Angeles Mayor Eric Garcetti

(Photo by Rodin Eckenroth/Getty Images,)

Rep. Seth Moulton (D-Mass.)

(Photo by Craig F. Walker/The Boston Globe via Getty Images)

New Orleans Mayor Mitch Landrieu

Albin Lohr-Jones/Pool via Bloomberg

Sen. Tammy Duckworth (D-Ill.)

(Photo by Scott Olson/Getty Images)

Washington Gov. Jay Inslee

(Photo by Karen Ducey/Getty Images)

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Onwards and leftwards

Throughout Clinton's book "What Happened," and in interviews over the last several days, Clinton argued that Sanders is not a Democrat. She alleged that he ran for the nomination not to help the party, but to "disrupt" it.

And by that measure, she says, he succeeded.

Mollineau argues that Sanders and others eager to challenge the party establishment "can't have it both ways."

"If you want to affect change within the Democratic Party than you need to become closer to the Democratic Party – you can't lob bombs from outside," Mollineau said, adding that while Sanders "could have been doing more to change the Democratic Party from within" throughout his years in Congress, "he just chose not to."

But while Clinton's career in public office is likely over, Sanders still remains a powerful force in national politics. For several months, he's held the mantle as the most popular politician in the country.

Many Democrats, including Jill Filipovic, an author and liberal commentator, argue that it is now Sanders' responsibility to unite the left.

"Sanders has positioned himself as a leader for the future of the left, and his followers agree, with near-messianic worship," Fillipovic wrote in a CNN column. "Embracing the whole left would be a good place for him to start."

But as Thomas Edsall pointed out in a recent New York Times column, there is evidence that progressives have only moved farther left since the election. He cites Pew Research Center data that shows that Democratic voters — particularly whites, Millennials, and post-grads — are much more eager to label themselves "liberal" in 2017 than they were in past years.

And while the left has seen a resurgence in support since November, the money and energy that's flowing into the party is going to Sanders' Our Revolution organization and the Democratic Congressional Campaign Committee, rather than the Democratic National Committee, which is suffering somewhat of a crisis of credibility post-2016.

While Mollineau admits that there are "ideological battles" that will likely be fought in the coming months and years, the tension between Clinton and Sanders won't necessarily remain central.

Although he doesn't put it past campaigns or super PACs to use lingering 2016 tension to "gain a tactical advantage" by aligning a candidate with Clinton or Sanders in an effort to alienate the others' supporters.

"It wouldn't surprise me, it's just a matter of how powerful that is and whether or not voters have moved on by then," he said.

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