What was basically inevitable after the March 15 primaries, when Hillary Clinton won all five contested states, is now all but official: Bernie Sanders, progressive insurgent candidate for the Democratic presidential nomination, has lost. New York was the death knell—he needed to win the state, and he lost handily. Only the die-hards are still professing belief now, and that belief has crossed the line from “optimistic” to “delusional.”

There’s only one way Bernie Sanders wins this thing, and that’s if one of Hillary’s dozens of scandals actually materializes into something disastrous. But the Clintons have been playing damage control on scandals for their entire political lives, and the odds that they’ll falter now, at the most critical hour, seem very, very small. Barring that sort of collapse, Bernie is buried—he’s too far behind in the popular vote and pledged delegate counts, and it’s about to get worse next week when Clinton runs the table (or comes very close) in the rest of the northeastern states.

So, there’s the elegy for his campaign straight from the mouth of a fervent supporter. I felt discouraged after March 15, but knew that if he won New York, the entire picture could change. He didn’t win. He didn’t come close. He didn’t even meet his soft target of 45 percent. Black voters destroyed him in the city, just as they destroyed him in the southeast at the start of the primary season, and Hillary’s coalition of minorities and women and old people held strong, while the young people that give Sanders his edge didn’t turn out in the huge numbers needed to reverse the outcome. This is an acknowledgement of defeat.

That being said, Bernie Sanders needs to stay in the race. Even with no hope of overall victory, he must march on through California. And the reason is simple: For the first time in decades, the American people have a chance to vote for a progressive politician, and to be at the vanguard of what hopefully becomes a lasting movement. Bernie skeptics have often said that his campaign is more about an idea than a candidate, and while I believe that his success refuted that point for some time—you don’t win 16 states and counting without posing a real threat to the frontrunner—it’s now factually true. The Sanders campaign has ceased to be about the 2016 presidential election, and is now about the future of the progressive movement.

There have been calls in some corners for Sanders to abandon the race, endorse Hillary, and unite the Democratic party ahead of the general election. This type of demand inevitably comes from those who never understood the Sanders campaign in the first place, and vaguely resented his ideals, and who tend to say things like, “from a policy perspective, there’s no difference between the two!”

Which is so agonizingly wrong. There are plenty who disagree, but for those of us who know in our hearts that Clinton is a free-trade war-hawk corporatist who co-opted enough of Bernie’s views to neutralize him in the primary but who will drop them like hot garbage the minute it’s expedient, this false equivalency is essentially heresy. I’m not going to get into the argument on a deeper level, since anyone who follows politics closely from either side has already been convinced, but believe me when I say that the Sanders coalition doesn’t now, and won’t ever, believe that the two candidates are the same.

Voters in all 50 states deserve the chance to vote for a progressive future. Sure, that vote is now symbolic. But they won’t have the chance to do it in November, and as the figurehead of progressivism, Bernie owes them that chance. He owes the Democratic party, which has done its best to screw him over from the start, absolutely nothing. And even if he did, it’s not within his power to unite us. His campaign has been about revealing the deep hypocrisy of the so-called people’s party, and now that it’s been laid bare, there is no going back. The Clintons have taken to the trenches to beat him, and he fought back (too late and too tepidly, in my opinion), and the idea of rapprochement is absurd. These people hate each other, and guess what? They should! Their policies are in diametric opposition.

After Hillary Clinton loses the general election, or wins and plods through a miserable four-year term, the time will come when progressive candidates have a real chance to win. The local and state races won’t feature huge national celebrities, or identity politics, or the machinations of the party elite and a pro-establishment media. As Bernie himself has said, real change has to come from the ground up, and when looked at from this perspective, his candidacy has always been about shining a light on the alternative path. He was never going to change things from the top down, and perhaps in time his supporters will understand that a Sanders victory wouldn’t have been good for the movement.

If progressivism is going to sweep the country, it has to start at the grassroots. What Bernie has done, in a candidacy that is headed toward a loss, is to paint the possibilities. The democratic-socialist ideas he’s been advocating no longer seem so far-fetched, and that’s a profound change of perspective for a country that has been embroiled in conservatism for 40 years. We needed to see this—we still need to see this, in all 50 states.

And that’s why Bernie must press on to the bitter end. There’s a famous Greek proverb that says, “a society grows great when old men plant trees whose shade they know they shall never sit in.” Sometimes it’s hard to see a person’s true purpose in the heat of battle, when everything becomes about wins and losses, but Bernie has been planting those seeds from the beginning. He may never see the fruits of his labor, but he knows what’s coming, and it’s his job now to spread the message to every corner of this country. His legacy, and the legacy of his ideas, belong to the future. That is a more important mission by far than uniting a broken party of the past.