You would think the far-left wing of the Democratic Party would have learned some humility in the wake of midterm elections in which candidates endorsed by Sen. Bernie Sanders (I-Vt.) were mowed down in primaries and more centrist candidates rolled up wins, taking back the House majority and grabbing a batch of governorships. You’d be wrong.

Jonathan Cowan and Matt Bennett of the centrist Third Way take exception with an assertion from New York Mayor Bill de Blasio (D) that “centrists got us nowhere.” Well, except the House majority, Cowan and Bennett point out, and all that goes with it (e.g. oversight hearings, passage of voting reform). They remind readers: “In the 2018 midterm elections, Democrats needed 23 seats to take control of the House, and they won 42. They also lost two, for a net 40-seat pickup. Of those 40, 33 had been endorsed by the moderate New Dem PAC. None of the 40 — not a single new pickup — was endorsed by far-left groups that de Blasio favors, like the Justice Democrats or Our Revolution. Zero.”

Whatever the merits of the left’s agenda (lots of free stuff), Cowan and Bennett argue, the political math doesn’t add up. The midterms prove it:

In Pennsylvania, the pragmatic Democratic Gov. Tom Wolf won reelection. And moderates Gretchen Whitmer and Tony Evers both won tough governors races in Michigan and Wisconsin. Before besting their Republican opponents, both also dispatched very liberal rivals in their primaries.
Indeed, those three gubernatorial campaigns offer Democrats a perfect roadmap for beating Trump in 2020. Hillary Clinton would be President if she’d won those three states, and she lost them by a combined total of just 70,000 votes. Whitmer, Evers and Wolf won two years later by a combined 1.3 million votes. They ran not on the promise of a Democratic Socialist revolution, but on kitchen table issues — health-care costs that are too high, good-paying jobs that are too scarce, even potholes that are too large. Whitmer’s bumper stickers said “Fix the Damn Roads!” and Evers used his opponent’s first name in dubbing the tire-killers of Wisconsin “Scott Holes.”

Those fretful that a Democratic nominee easily labeled as a wide-eyed radical could hand the election to President Trump know that ideological purity makes for bad politics. It’s no fluke that Trump spent some of his State of the Union address raising the boogeyman of socialism, Venezuela-style. (Actually, Third World, corrupt authoritarianism aptly describes his administration.) Even he can figure out that Republicans can win in competitive races only when they can paint Democrats as left-wing kooks. (Look at the Ohio governor’s race, where Richard Cordray lost, as opposed to the wins by the moderate governors noted above.)

Amy Walter of the Cook Political Report observes, “Privately, lots of Democratic insiders also fear that the only thing standing between Democratic victory in 2020 and another Trump term is a nominee who scratches the itch of the liberal base but can’t appeal to the moderate middle.”

Is there a danger that Democrats will blow it in 2020 by going too far left? Without Sanders and de Blasio in the race, there doesn’t seem to be any shortage of energy, conviction and bold policy ideas. Some possible contenders seem to have an inkling that the general electorate in November 2016 will look nothing like New York City or Vermont. (Democrats have those places locked up and are ready to crawl over glass to get rid of Trump; it’s the rest of the country they must worry about.) Sens. Sherrod Brown (D-Ohio) and Amy Klobuchar (D-Minn.) made clear they want to expand health-care coverage however they can, not insist on immediate eradication of private health-care insurance.

Democratic contenders in 2020 would be wise to adopt a few basic rules. These should prevent them from going over the left edge of the party while maintaining comity in a party that will need to unify after a spirited primary.

First, they shouldn’t have fights with de Blasio or anyone else over labels and ideological one-upmanship. (Socialists bad! No, centrists are losers!) This is entirely unproductive, indeed meaningless, when no one defines their terms. Democrats would be smart to debate policy ideas (let others label them) and make the case as to why they are better suited to beating Trump and then governing effectively. Former Indiana governor Mitch Daniels (R) liked to say that he wouldn’t tell voters, “Here’s a Republican idea!” He’d tell them about the idea. A Democratic candidate shouldn’t advertise her ideas as the most progressive or the least progressive, but rather as the best out there.

Second, don’t sign on to bumper stickers. (Medicare for All! The Green New Deal!) This only empowers the far left to set the terms of the debate and exempts the far left from explaining and defending flawed policies. Why not come up with their own ideas, ones designed to unify the party and appeal to non-Democrats? You don’t have to sign on to pie-in-the-sky bills that will never get a vote, even in the House, to stake out support for solutions to climate change, worker dislocation and more.

As to the Green New Deal, Jonathan Chait explains: “On the policy, the Green New Deal simply outlines ambitious targets for carbon reductions, without delving into specifics as to how the targets will be met. In place of detail it offers optimism. Noting that the International Panel on Climate Change proposes to cut global emission by 40 to 60 percent by 2030, and get to net zero by 2050 — which is itself a heroic goal — the Green New Deal proposes the United States get to net zero emissions by 2030.” Signing on to that sort of document without a firm grasp of why it’s politically and substantively unwise (actually, impossible) suggests a lack of judgment by those claiming the power to bring the country together. Candidates set themselves up for trouble when they take seriously something just about everyone knows isn’t serious. (“America won’t get 100 percent of its power from zero-emissions sources within a decade, either, another audacious Green New Deal goal,” writes Michael Grunwald. “And we’re not going to upgrade the energy efficiency of every single building in the country, as the resolution proposes. If we were getting all our energy from zero-emissions sources, it wouldn’t even make sense to try.”)

Third, those who aren’t on the fringe of the party need to reject the tag that they are “mushy” moderates. Bold moderation and clear, fact-based reforms with wide support that get at the heart of our biggest problems shouldn’t be a bad thing. The goals that virtually everyone in the field has set — expanding health care, combating global warming, equalizing educational opportunities, passing comprehensive immigration reform, enacting gun safety laws — are very popular. What’s not popular is the most extreme, unrealistic incarnation of these goals. They should take comfort in knowing that polls show Democratic voters much more concerned about winning than ideological purity.

Democrats who have entered the 2020 race aren’t running to be mayor of New York or a senator from Vermont. They’re running for the nomination of a party that has to appeal to a big, diverse and contentious country. Democratic primary voters seem to understand this, even if some party activists do not. Democratic contenders best not crawl out so far on a limb that they won’t be able to scamper back when Election Day 2020 rolls around.

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