Some politicians and commentators say that Bernie Sanders is losing leverage because he hasn't conceded the primary to Hillary Clinton. To believe that is to misunderstand both the candidate and his supporters. Sanders received a mandate in "defeat" that most politicians never achieve in victory.

The calls to surrender reached a fever pitch before the last primary even ended. We were told that Sanders was being stubborn, that he was rapidly losing influence. It was even said that all of the convention's prime-time speaking spots would be taken if he didn't concede soon, as if they were reservations at Nobu and he had no pull with the maître d'.

If Bernie were denied a prime-time slot at the convention, chaos would ensue. You can be sure that whenever and however the deal is struck, they'll make room for him at a peak viewing hour.

The Clinton team's impatience is understandable, even if it lacks a certain grace. But they're misreading both Sanders' nature and the nature of the negotiations now underway. So is the New York Times' Nate Cohn, who tweeted:

"A fun thought experiment: Imagine Sanders winning but Clinton refusing to endorse unless he adopted her views, etc."

That thought experiment would make sense in a typical primary campaign. But this year is different. Even without context, the raw numbers are impressive.

Leverage? As New Yorkers used to say, I got your leverage

:

12 million votes

Victory in 22 states

45 percent of pledged delegates

A history-making small-dollar fundraising campaign that outraised his well-heeled opponent

And all while facing one of the most powerful Democratic clans in history, rejecting big-money donors, and challenging one of the most famous people in the world as a leftist outsider.

Leverage? Consider the trend line: Twelve months ago Bernie Sanders was all but unknown nationally. He didn't fit the typical "politician" profile in age, style, or rhetoric. He was a self-described democratic socialist. And he faced overwhelming obstacles erected by the party machinery at all levels.

Memories are short. When Sanders announced his run in April 2015, FiveThirtyEight's Harry Enten said he was "almost certainly not going to be the Democratic nominee for president in 2016." Enten added:

"Hillary Clinton is the most dominant non-incumbent front-runner in modern primary history."

"It would take a truly special candidate to defeat her," he continued, "and Sanders ... is not the politician for the job."

That was what pretty much everyone thought. Look what happened.

There's no need to relitigate all the roadblocks Sanders faced, at least not now. It's enough to say that the success he achieved, against overwhelming odds and "the most dominant non-incumbent front-runner in modern primary history," affirms the power of his message.

Sanders also won the hearts of Democratic voters - more so than his opponent, in fact, despite her thirty-year head start. A recent Gallup poll found that Sanders "continues to be significantly more popular than Hillary Clinton," among members of the party he only joined last year.

Sanders' current net favorable rating among Democrats is 13 points higher than Clinton's, according to a recent Reuters/Ipsos poll. The same poll found that 75 percent of Democrats want him to play a "major" role in their party. (Surprisingly, 44 percent of Democrats polled wanted Sanders to run as an independent, a fact that should give the Clinton team pause.)

And Sanders' stunning margins among young voters tell us that he isn't just speaking for a large percentage of the Democratic Party's voters. He also speaks for its future.

Clinton needs his supporters. As Nate Silver noted last month, "her lack of support from Sanders voters is harming her general election numbers." A YouGov/Economist poll in late May found that "Only half (50%) of Sanders supporters pick Clinton over Trump in the general election trial heat."

While those numbers are likely to keep falling, these voters can't be handed off to Clinton and her party like a football. They are deeply skeptical about her, and not without reason. It will take concessions to win their support. And those concessions -- especially on popular issues like tuition-free higher education, Wall Street reform, and Social Security -- will make the Democrats a stronger party.

I have no inside information, but it seems pretty obvious that Bernie Sanders isn't positioning himself for another run. He's not being stubborn, he's negotiating. Nobody concedes while the negotiations are still going on. His negotiating partners should stop demanding that he fold his cards before the dealing's done.

They should also understand that they're not just dealing with a candidate. They're also talking to the representative of a movement, one that could decide the fate of this election and the future of their party.

As leverage goes, that's about as good as it gets.