U.S. President Barack Obama and Democratic Nominee for President Hillary Clinton leave the stage at the Democratic National Convention in Philadelphia, Pennsylvania, U.S. July 27, 2016. REUTERS/Scott Audette

For the first time in a quarter-century, we're about to see a vacuum of political and intellectual leadership in the Democratic Party. An entire generation of leaders -- including Barack Obama, Joe Biden, and Bill and Hillary Clinton -- will be leaving the political stage. With them will go an entire infrastructure of policy advisers, political strategists, associates, friends, and hangers-on.

The party will have to remake itself. The question is, as what?

"I think there's going to be a fight in the Democratic Party about which direction to go in," political consultant Joe Trippi told the Washington Post. "That's healthy for the party long-term, but it's going to be painful over the next few years."

Painful for some, perhaps, but not for everybody. Some people are likely to be energized by the opportunity to inject new blood into an ossified party leadership.

These are hurtful times, to be sure. The Trump years are going to be grim - very grim - for millions of people. Democratic voters are saying goodbye to leaders they've known and liked for many years. Democratic politicians are in the minority in most state legislatures, only hold 18 governors' seats, and haven't had so little power in Washington since 1928.

But the political purgatory of 1928 was followed by the election of 1932, when Democrats gained control of all three branches of government. They took more than 100 House seats and 12 Senate seats from the GOP, and Franklin Delano Roosevelt became the most transformative president of the twentieth century.

The parallels aren't't exact. The Republicans' pre-1932 victories were due primarily to that era's prosperity, and the Democrats' win to the shock of the Great Depression. It would be both ghoulish and foolish to hope for a repeat of that scenario. These aren't prosperous times (although a major Trump recession or depression is certainly possible). But the 1928-32 election cycle showed us how much can change in only four years.

It doesn't always take a catastrophe to reverse political fortunes. Conservatism was at an all-time low in 1964. Post-war Democrats and Republicans built a consensus around liberal ideas on issues like infrastructure spending (Eisenhower built the federal highway system), unionization, and Social Security. Barry Goldwater's 1964 defeat was widely considered conservatism's death knell.

Four years later Richard Nixon won the presidency with a culturally conservative message. Sixteen years later Ronald Reagan became the 20th century's second-most transformative president, ushering in a new era of economic conservativism.

Most political observers in 1964 would have advised Republicans to stick to a center-left agenda. Instead, conservatives crafted a narrative that - although profoundly wrong on the issues - transformed politics by speaking to many voters' economic, moral, and social concerns.

Now it's the left's turn.

Polls already show that the public largely supports the left's ideas on Social Security expansion, Medicare, the minimum wage, Wall Street, taxing the wealthy, and other key issues. But too often the Democratic Party has been constrained by the equivocation of its leaders, and by an intellectual class reluctant to embrace new ideas.

The Affordable Care Act is a case in point. It has helped millions, and its repeal would be a tragedy. But, as Sen. Elizabeth Warren reportedly said this week, "Let's be honest: It's not bold. It's not transformative."

Warren continued: "I'm OK taking half a loaf if our message was 'Here's half, now let's go get the rest.'"

Instead, voters struggling with sky-high medical costs found themselves being lectured on why they should feel grateful instead. And when Bernie Sanders electrified audiences by calling for Medicare for All - which has been successfully implemented in every other developed country on Earth, in one form or another - most of the Democratic intellectual class insisted it couldn't be done, even as its own predictions for the ACA were proving false.

Sen. Warren also reportedly said that Democrats had become too close to corporate interests and too distant from working people. "That's where we failed," she is quoted as saying, "not in our messaging, but in our ideology."

That's exactly right. No amount of ginned-up speechwriter phrases ("trumped up trickle-down") can sell voters on an agenda that doesn't speak to their needs, or on Rube Goldberg-ish policy prescriptions that mistakenly rely on the power of "markets" and "competition."

"Ideology" is not a dirty word, although a lot of people in the Democrats' outgoing political and intellectual classes tried to make it one. They claimed to be technocrats, free of any ideological taint. But that was nothing more than a smokescreen for their own biases (and undoubtedly, in some cases, for the interests of their funders).

The new Democratic Party will need to broaden its intellectual horizons. And it will need to draw energy and inspiration from a growing wave of independent movements: for racial justice, economic change, rational foreign policy, renewal of democracy, and broad social equality.

This is a time to think big. It's time to comprehensively address climate change, which will get even worse under Trump; to work on making Medicare available to every American; to address the nation's growing retirement crisis, by increasing Social Security's benefits; to provide tuition-free higher education; to guarantee jobs for everyone willing to work; and to begin addressing the other great challenges of the 21st century.

The next four years will be painful, especially for the most vulnerable among us. But the struggle for a better future needn't be. In fact, many people have already found that it gives meaning and purpose to their lives.

The Bernie Sanders campaign reminded us that people will fight for a cause. The Democratic Party needs to become a cause more people want to fight for. In the midst of defeat, it has that chance.