Bernie Sanders is wading into the civil war over the Democratic Party's future, criticizing his "corporate" colleagues who have blamed progressive policies for their spate of losses in the 2020 election. 

"With the blame game erupting, corporate Democrats are attacking so-called far-left policies like Medicare for All and the Green New Deal for election defeats in the House and the Senate," Sanders wrote in an op-ed for USA Today. "They are dead wrong."

While Democrats will maintain control of the House, their majority will shrink by at least six seats next year, making it the thinnest in decades. At the same time, Democrats picked up just one seat in the Senate, where control hinges on two January runoff races in Georgia. If Democratic candidates win both of those races, they would secure a 50-50 split, with Vice President-elect Kamala Harris able to cast a tie-breaking vote.

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In the week since the election, Democrats have traded blame over who's ultimately responsible for the lackluster showing. Moderates have pointed fingers at their colleagues who embraced the "defund the police movement" and for not pushing back harder against socialism. 

But progressives have argued those liberal policies help to galvanize the party's core base and are popular among the general electorate — a sentiment that Sanders, a self-declared democratic socialist, echoed. 

2020 presidential candidates Senator Elizabeth Warren, a Democrat from Massachusetts, left, Senator Bernie Sanders, an Independent from Vermont, and former Vice President Joe Biden, arrive on stage ahead of the Democratic presidential debate in Charleston, South Carolina, in February 2020. Photographer: Alice Keeney/Bloomberg via Getty Images

2020 presidential candidates Senator Elizabeth Warren, a Democrat from Massachusetts, left, Senator Bernie Sanders, an Independent from Vermont, and former Vice President Joe Biden, arrive on stage ahead of the Democratic presidential debate in Charleston, South Carolina, in February 2020. Photographer: Alice Keeney/Bloomberg via Getty Images

Sanders, who ran for president in 2016 and 2020, noted that 112 co-sponsors of Medicare-for-all were on the ballot last week, and all of them won their races. Ninety-eight co-sponsors of the Green New Deal were up for election, and only one lost.

"It turns out that supporting universal health care during a pandemic and enacting major investments in renewable energy as we face the existential threat to our planet from climate change is not just good public policy," he wrote. "It also is good politics."

The Vermont senator, an independent who caucuses with Democrats, also pointed to progressive ballot initiatives that passed last week, including a $15-an-hour minimum wage hike in Florida; 12 weeks of paid family leave in Colorado; marijuana legalization in New Jersey, Arizona, Montana and South Dakota; and a tax increase on Arizonans earning more than $250,000. 

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"The American people are sick and tired of seeing billionaires and Wall Street become much richer, while veterans sleep out on the streets, our infrastructure crumbles and young people leave school deeply in debt," Sanders argued. "They want a government that works for all, not just the few. That’s the right thing to do, that’s the moral thing to do and, for the Democratic Party, that is the way to win elections."

The battle between progressives and moderates is likely to escalate in the coming weeks as President-elect Joe Biden looks to build his Cabinet. Progressives have pushed Biden to tap Sanders as his Labor secretary, a job that the senator indicated he's willing to take. 

"What's true is I want to do everything I can to protect the working families of this country who are under tremendous duress right now. Whether that's in the Senate, whether that's in the Biden administration, who knows?" Sanders said during an appearance on CNN. "Let's see how that unfolds."

Still, Democrats have privately conceded that if Republicans retain control of the Senate and Mitch McConnell remains majority leader, the progressives have no chance of confirmation.