Bernie Sanders addresses supporters in New York on June 23. (Craig Ruttle/AP)

Bernie Sanders effectively articulated a set of progressive values and issue positions that energized younger voters and the Democratic Party’s left. That earned him kudos for his passion and electoral success.

Even more important, Sanders’s performance during the presidential nominating process gave him leverage with Hillary Clinton, the presumptive Democratic presidential nominee, who has wanted Sanders’s enthusiastic endorsement for weeks.

But instead of using that leverage when it was at its peak, Sanders bungled the greatest political opportunity he will ever have. Instead of getting on board with the Clinton campaign, the former mayor of Burlington, Vt., and current member of Congress hesitated, resisted, dithered and shilly-shallied.

Now, after Clinton has opened up a significant advantage in general-election ballot tests over Republican Donald Trump, a Sanders endorsement will be anticlimactic, welcomed by Clinton but certainly not the blockbuster it would have been even a few weeks ago.

Why the change? Because Clinton doesn’t need Sanders anymore.

At least not the way she once needed his embrace. The former secretary of state has an enthusiastic endorser that is even better than Bernie: Elizabeth Warren, the senator from Massachusetts whose populism and charisma excite the same people who supported Sanders during the primaries and caucuses.

[Clinton and Warren electrify voters on the stump]

Apparently, getting five Sanders supporters on the Democratic National Committee’s platform committee wasn’t enough for the senator from Vermont. He still wants more. Of course, he always wants more. Whether it is ego, vanity or simply a political miscalculation, Sanders has over-read his mandate.

When asked on MSNBC June 24 if he would vote for rival Hillary Clinton, Democratic presidential candidate Bernie Sanders answered, "Yes." Sanders says he's focused on beating Republican Donald Trump. (Reuters)

Speaking to CNN’s Jake Tapper on Sunday, Sanders explained that he is still fighting Clinton because, although the platform committee arrived at many mutual agreeable compromises, he wants his party to take stronger stands on a number of issues:

“We’re going to take that fight to Orlando, where the entire committee meets in two weeks. And if we don’t succeed there, we are certainly going to take it to the floor of the Democratic convention. And that is what this discussion in St. Louis did not include, as you indicated — the need to deal in a very strong way with the crisis of climate change.

“We need a tax on carbon. We need to end fracking. We need to be very, very clear that the minimum wage must be raised to $15 an hour. In my view, we need a Medicare-for-all, singer-payer program. So, we have made some good gains, and I want to thank all of the people who participated in that process. We have more to do.”

What Sanders doesn’t seem to understand is that Clinton won the Democratic nomination. She did that by getting more votes than he did.

[Bernie Sanders just gave an amazingly condescending interview about Hillary Clinton]

Sanders pushed his agenda for months, contrasting his priorities and values with Clinton’s. Yet Democratic voters gave her more votes and more delegates. Now, Sanders is fighting for a platform that Clinton must run on. In other words, he is trying to win through the platform what he couldn’t at the polls.

Sanders is not yet irrelevant. But he is moving in that direction. The longer he delays endorsing Clinton, the pettier and smaller he seems. In fact, he reached a point weeks ago when his stubbornness became counterproductive.

Like the professional athlete who has arrived at the end of the line, his skills having deteriorated and his reputation sinking because he insists on suiting up for yet another season, Sanders increasingly is a man in denial.

No, Sanders isn’t merely running for president. He is running to change the Democratic Party (to which he hasn’t even belonged) and to bring his progressive, democratic-socialist values to America. But the Vermont independent ought to realize that the Democratic Party also includes Sens. Heidi Heitkamp (N.D.), Jon Tester (Mont.) and Joe Manchin (W.Va.). Indeed, they’ve been part of the party longer than he has.

Delaying a full-throated endorsement of Clinton until delegates arrive in Philadelphia won’t make Sanders more influential. It will merely make him look irrelevant and delusional.

Whether he realizes it or not, his moment has already passed.