James Downie is The Post’s digital opinions editor.

One of the great ironies of the American political process in the 21st century is the Democratic Party superdelegate. On campaign finance reform and voting rights, the party fights to give regular Americans more of a voice. Yet when it comes to choosing a presidential nominee, it’s the Democrats, not the Republicans, who give 712 party insiders roughly the same influence as 5.5 million ordinary voters in Texas, Florida, Ohio and Michigan.

And for the second contested presidential primary in a row, these superdelegates are playing an important role. Though Sen. Bernie Sanders (I-Vt.) has been far more successful than many in the establishment thought possible, it will be difficult for him to overcome Hillary Clinton’s 200-strong lead among pledged delegates. But Clinton’s 400-plus lead among superdelegates takes the task of Sanders winning the nomination from challenging to nigh impossible.

The power of the Democratic superdelegates should serve as an inspiration to Sanders supporters thinking about what comes next if — as seems likely — the senator falls short. Whether or not they like the superdelegate system, the party establishment wrote the rules long before the first ballot was cast. This shows the importance of having a presence in the corridors of power. Berners should be looking ahead right now to changing the rules — and the establishment itself — in 2020 and beyond.

Are the young voters propelling Sanders ready to remake the Democratic Party in their own image? The benefits of a better, more progressive party on the American left would go far beyond matters of rule-making. It would also mean a party whose priorities reflect its voters more than its donors. Sanders’s supporters have demographics on their side. Younger voters aren’t just breaking slightly against the Democratic establishment; they are overwhelmingly against it. Sanders has repeatedly received a clear majority of voters under 45, and 70 to 80 percent of voters under 30. Their power in the party is only going to grow.

You've probably heard the term "superdelegates" recently – but what is a superdelegate, and why do they matter in this election? (Peter Stevenson/The Washington Post)

And the Democratic establishment is due for a makeover. Consider the party’s leading figures: Aside from President Obama (age 54) and Democratic National Committee Chair Rep. Debbie Wasserman Schultz (49), you have Clinton (68), Sens. Harry M. Reid, Charles E. Schumer and Elizabeth Warren (76, 65, 66) and Reps. Nancy Pelosi, Steny H. Hoyer and James E. Clyburn (76, 76, 75). Almost all of them will be retired or headed in that direction 10 years from now, leaving a vacuum that younger leaders can fill.

There will be those on the progressive left reluctant to enter the heart of what they see as a fundamentally corrupt two-party system, preferring instead to try to force reform either through the ballot box or by avoiding the conventional political process altogether. But the last major leftist movement to alter the political conversation — Occupy Wall Street — faded as a political force largely because so many participants rejected getting involved in electoral politics. As for the ballot box, the young people behind Sanders must do a better job of voting in nonpresidential elections. Eight years ago progressives backed Barack Obama, and the disappointments to progressives of his administration — the lack of prosecution of Wall Street, the expansion of the drone war, etc. — show that winning a presidential election won’t change a party by itself.

Sanders supporters should not only refuse to give up on the political process but also double down on fighting for the future of the Democratic Party. That means more than just showing up to vote; it also means running for office and joining party organizations. There are a few examples of Sanders-aligned House candidates this cycle — such as Zephyr Teachout in New York and Tim Canova in Florida — but in the long run, more congressional, state and local candidates will be needed. Ultimately, that’s the best way to make sure that the momentum from Sanders’s success doesn’t fade away.

To be clear, this does not mean every activist needs to leave their organizations to run for a local DNC chairmanship or work entirely within the Democratic Party framework. True change requires both inside and outside pressure — those working within the corridors of power to alter the status quo with others amplifying the popular pressure outside. Too often, though, young voters have shown a tendency to make smart criticisms of institutions yet decline to do the hard work of changing those institutions — or even voting.

Turning the “new left” into the new Democratic establishment is not something that has always been achievable in U.S. politics. For decades, the American center fell, on many issues, to the right of the center in other countries. But demographics and Sanders’s success suggest the potential is now there to truly make the Democratic Party more progressive. It would be a shame if his supporters, despite losing this battle, missed their chance to win the war.