Photo: Win McNamee/Getty Images

Here is a science-fiction scenario: Imagine a strange new virus that incapacitates everybody below the age of 75. The virus wipes out the entire political leadership, except one old man, who has survived on account of his age, but may also be too old to handle the awesome task before him.

Now suppose — and I am not certain this is the case, but just suppose — that this is happening to the Democratic presidential campaign. The virus is Twitter, and the old man is (duh) Joe Biden.

In the aftermath of the 2016 elections, an exotic political theory promoted by the party’s most left-wing flank suddenly gained wide circulation. The appeal of Bernie Sanders proved Democrats were ready to embrace socialism, or at least something close to it; and Donald Trump’s election proved a nominee with extreme positions could still win. These two conclusions, in combination, suggested the party would move as far left as activists preferred at no political cost.

Neither of these conclusions was actually correct. The Bernie Sanders vote encompassed voters who opposed Hillary Clinton for a wide array of reasons — including that she was too liberal — and were overall slightly to the right of Clinton voters. And political-science findings that general election voters tend to punish more ideologically extreme candidates remain very much intact. (Trump benefited greatly by distancing himself rhetorically from his party’s unpopular small-government positions, and voters saw him as more moderate than previous Republican nominees, even though he predictably reverted to partisan form once in office.)

And yet, this analysis seemed to race unchallenged through the Democratic Party from about 2016 — it seemed to influence Clinton, who declined the traditional lurch toward the center after vanquishing Sanders — through this year. Through sheer force of repetition, it achieved the status of a kind of self-evident truth:

My 'interactions' are full of people asserting things like: there are no swing voters; the only thing that changed in 2018 is turnout, Democrats can't and haven't won over any Trump voters. And whatever you think of the optimal strategy for Democrats, this is all facially untrue — Nate Cohn (@Nate_Cohn) September 10, 2019

By the beginning of 2019, most of the Democratic field had absorbed this new conventional wisdom. The field was racing left, treating the consensus on progressive Twitter as though it were a simulacrum of the real Democratic Party. On some issues, like a higher minimum wage and more generous Social Security benefits, bold left-wing positions really do capture strong political majorities. But on other issues, many candidates have exposed themselves to damaging general election attacks: on reparations for slavery, decriminalizing the border, and giving health-care coverage to undocumented immigrants, among others.

Here is Kirsten Gillibrand rattling off social-justice lingo last month:

I don’t believe that it’s the responsibility of Cory and Kamala to be the only voice that takes all of these issues of institutional racism, systemic racism in our country. I think as a white woman of privilege who is a U.S. senator running for president of the United States, it is also my responsibility to lift up those voices that aren’t being listened to. And I can talk to those white women in the suburbs that voted for Trump and explain to them what white privilege actually is, that when their son is walking down a street with a bag of M&Ms in his pocket wearing a hoodie, his whiteness is what protects him from not being shot.

It was a perfect encapsulation of Gillibrand’s campaign, which seemed to be positioning the candidate to be elected President of Twitter. Her campaign posted the clip and got more than 1,000 likes, as well as favorable coverage of the remarks in outlets like Vox, Mother Jones, and the New York Times op-ed page.

A certain number of activists thrilled at the sight of a presidential candidate using the concepts and terms of the social-justice left. As a messaging strategy for building an electoral majority, though, it could charitably be called risky. None of the 40 Democrats who flipped Republican House districts in 2018 ran on a message of calling out white women for their privilege. Not long after this apparently triumphal moment, Gillibrand had to drop out of the race.

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Nowhere was the gap between perception and reality more dramatic than on health care. In the run-up to the primary, most of the field signed on to Bernie Sanders’s Medicare for All plan. Sanders had not managed to work out solutions to the obstacles that have bedeviled single-payer health-care supporters for decades: How to assure Americans who currently have employer-sponsored insurance to accept higher taxes and that they’ll be happier on a public plan.

Kamala Harris has had second thoughts, and has twisted herself into a pretzel trying to wriggle away from the proposal. Cory Booker has largely avoided discussing it. Elizabeth Warren was signaling last year that she would support more moderate reforms, but has instead handcuffed herself to the Sanders plan.

The vulnerabilities of this position have been on bright display in every Democratic debate. Neither Warren nor Sanders could supply a coherent response to the question of whether middle-class voters would pay higher taxes or whether they would like being moved off their employer plan. “I’ve never met anybody who likes their health-insurance company,” Warren insisted, eliding the clear reality that most people who have employer-sponsored insurance do like it. When asked about higher taxes, they dodged by changing the question to total costs. And while it’s probably true that they could design a plan where higher wages — by taking insurance off the company books — would cancel out the high taxes, neither inspired confidence that they could persuade skeptical voters they’d come out ahead in the deal.

The odd thing about this race to the left is that there’s little evidence it appeals to the primary electorate, let alone the general election version. Democrats strongly support universal coverage, but have lukewarm feelings on the mechanism to attain this. They prefer reforms that involve a combination of public and private options over the Bernie movement’s manic obsession with crushing private health insurance.

This applies as well to the party’s general ideological orientation. More Democratic voters express concern the party will nominate a candidate who’s too liberal (49 percent) than one who’s not liberal enough (41 percent). By a similar 54–41 margin, more Democrats want their party to move toward the center than toward the left.

“Responding to a Democratic electorate that has been radicalized by Donald Trump and is still smarting from the 2008 recession, Warren and Sanders have yanked the conversation — and the party — sharply to the left,” exults The Nation’s Jeet Heer, treating the premise that Democratic voters demand a leftward tilt as so self-evident he needn’t bother substantiating it. “Politicians often deemed moderate such as Pete Buttigieg and Kamala Harris have joined the policy arms race, with candidates trying to top one another with their competing plans to remake America.”

The metaphor “policy arms race,” which he borrows from Paul Waldman, is worth lingering over. An arms race is a dynamic in which competitors are forced to devote more of their resources to defense lest they fall behind. It is a negative-sum dynamic, in which both sides are trapped into harmful behavior. Even hawks like Eisenhower, Nixon, and Reagan recognized the inherent dangers of an arms race.

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A recent Politico story by Ryan Lizza conveys the frustration Biden’s campaign feels with the news media, which generally reflects the cultural and, to a lesser extent, ideological perspective of the party’s activists. They complain the coverage has drawn a portrait of Biden as a stumbling loser, surviving on a combination of name recognition and Obama nostalgia, fighting off the party’s rising progressive tide.

There is some real merit to this complaint — especially the notion that “ideas” are an exclusive asset of his opponents. It seems just as likely that many of Biden’s supporters have a positive appreciation for compromise and pluralism, designing policies that appeal to wide social and economic swaths of the country, rather than those that draw sharp cleavages between winners and losers.

But if Biden has this ideological territory to himself, it raises the possibility he could win the nomination simply because his opponents abandoned the field. What if all his major competition raced to the left, succumbing to the fashionable delusion that the party rank and file demanded a Bernie-like nominee? And what if the only self-styled moderates in the race (Michael Bennet, Amy Klobuchar, John Hickenlooper, and so on) lacked the name recognition to mount a credible challenge?

Indeed, two candidates seem to have realized this problem. Kamala Harris and Cory Booker have dropped out of the left-wing arms race and begun positioning themselves as heirs to the Obama style of optimism and uplift. But it’s already getting late, and each candidate has already devoted most of the time between their launch and the Iowa caucuses trying to avoid getting dragged on Twitter. What’s more, the fact that both Harris and Booker are trying to squeeze into the same political space increases the probability that neither will achieve escape velocity.

Meanwhile, Biden looks like a candidate hoping to somehow stagger across the finish line. He has campaigned at a leisurely pace. His first debate performance was disastrous. The next two started out vigorous, but saw him slowly flag as the evening wore on. Thursday night included a rambling answer in which he urged parents to “make sure you have the record player on at night.” Biden’s lack of awareness of Twitter may be to his benefit, but it’s more disturbing if he lacks a working knowledge of such innovations as the compact disc player.

If Biden isn’t up to this, he needs to collapse soon enough for another mainstream liberal Democrat like Booker or Harris to take his place. Yet it’s at least as easy to imagine he will stay in the race, locking down the party’s center, while Sanders and Warren continue to try to outflank each other on the left. There’s still some time for the race to change. At the moment, the most dire scenario looks disconcertingly real.