Only the downtrodden and dispirited Democrats could work themselves into a bout of I’m-on-the-ledge-and-thinking-about-jumping depression over the failure of a 30-year-old first-time candidate to win a House seat in a Georgia district where he didn’t even live.

Equally ludicrous are the recriminations over Democratic tactics in Georgia-6. Last Tuesday’s special election in the upscale Atlanta suburbs might be a bellwether if it were typical for both sides to spend $50 million on a single House race. At that rate of spending, the 2018 House races would cost about $21 billion.

The Donald Trump presidency is so peculiar and the times are so volatile that it is difficult to predict what the mood will be on Election Day 2018. Who knows if congressional candidates in 16 months will be battling over health care, the economy, Russia, impeachment or impending war with North Korea?

An identity crisis

But what is undeniable is that the Democrats are long overdue for a period of reckoning about who they are and what they represent. The problem is not messaging, consultants or Nancy Pelosi. It is that the Democrats (and, yes, that definitely includes Bernie Sanders) have to wave good-bye to the 20th century

The tangled history of two roughly similar words — “liberal” and “progressive” — defines the Democrats’ current dilemma.

Pressed to defend her tenure as Democratic leader at Thursday’s press conference, Pelosi univocally declared, “I am a progressive.”

Sanders has frequently repeated the refrain, “We need a Democratic Party that is not a party of the liberal elite but of the working class of this country.”

Ask almost any Republican member of Congress about his or her ideology, and you will get a variant of “I am a proud conservative.” Inquire about a Democrat’s political philosophy — and you will get anything from a speech about “progressive values” to a discourse on how “labels really don’t really describe who I am.”

It wasn’t that long ago when most northern Democrats happily identified themselves as liberals, casting themselves in the mold of Franklin Roosevelt, Harry Truman and John Kennedy.

But all that began to change in the 1980s under an assault from Ronald Reagan and TV attack ads lambasting Democratic candidates as “liberal, liberal, liberal” and “dangerously liberal.”

Suddenly, Democrats reinvented themselves as “progressives” as if Woodrow Wilson were back on the ballot. As liberal columnist Michael Kinsley mockingly put it in 1988, “In the 1950s, the term progressive was used by Americans who didn’t want to admit to being Communists. Today it’s used by people who don’t want to admit to being liberals.”

Thus were born the politics of the defensive crouch. Triangulating with gusto after the 1994 failure of his health-care plan, Bill Clinton tried to blunt the standard Reaganite critique of Democrats by embracing balanced budgets, welfare reform and tough anti-crime policies.

Barack Obama, who inherited the worst economic crisis since the Depression, did not have the luxury of treading cautiously. But his proposed 2009 stimulus package was smaller than many economists recommended and his health-care plan, with its emphasis on markets and incentives, was initially conceived in the naive hope of winning some Republican support.

Hillary Clinton — who like her husband was shaped by the three GOP landslides of the 1980s — embodied the dangers of combining Democratic political caution with a lack of personal charisma. As a result, it is already hard to remember a single major policy animating her 2016 campaign.

All of this is not a brief for Sanders, who is as mired in 20th-century politics as the Clintons, Chuck Schumer and Pelosi.

The Sanders vision for the Democrats (free college tuition, Medicare for all) is Great Society liberalism untempered by any awareness of the excesses that led to Reagan’s rise. In Bernie’s vision for America, policy implementation doesn’t matter as long as your heart is pure.

Yes, Democrats have tilted too close to Wall Street with the deregulatory zeal of the Clinton years and a continuing obsession with the deficit. But that doesn’t mean that every governmental initiative can be paid for by taxing “the 1 percent” or that all such soak-the-rich proposals represent wise tax policy.

Trump captured something lacking in the Democratic vision with his recycled 2016 campaign slogan, “Make America Great Again.” There is a prevalent sense of national decline. Since the 2008 economic collapse, roughly two-thirds of Americans have consistently believed that the country is on the wrong track.

A new agenda

What the Democrats need is an agenda to update John Kennedy’s 1960 mantra: “Let’s Get This Country Moving Again.” (Yes, this harks back to the 20th century, but the slogan has lasting appeal).

With the Republicans going off the rails with Trump, the Democrats have a chance to emerge as the Adult Party in America with solutions that cut across stale ideological lines.

There should be a way, for example, to revive public schools without making the Democrats the party of the teachers’ unions. There should be a way to rebuild our roads and airports without enriching Wall Street investors. And there should be a formula for a health-care system more workable than Obamacare, but not a slavish extension of the 1965 Medicare legislation.

Only one thing is worse for the Democrats than doing nothing to revamp the party for the 21st century. And that is to buttress Trump by continuing the self-destructive folly of bitter proxy battles between the establishment and insurgent wings of the party.