WASHINGTON _ Even with his path to the Democratic presidential nomination rapidly disappearing, Bernie Sanders couldn't bring himself to publicly accept defeat. Along the way, he overplayed his hand and squandered the political capital he'll need to force policy and procedural reforms on the Democratic Party, according to allies and party strategists.

"We're already way past the maximum point of leverage that he and his movement built up. It's definitely dissipating every day," said Joe Trippi, a Democratic strategist and veteran of presidential campaigns.

Trippi put the high point of Sanders' clout at April 9, after he won seven straight contests ending with Wyoming. But he lost seven of the last nine contests, walloped by 58 points in the District of Columbia, which held the final primary of the season on Tuesday. Hillary Clinton already had locked up the nomination with a decisive victory in California a week earlier, and some of the highest profile Sanders supporters _ including Sen. Jeff Merkley or Oregon, Rep. Raul Grijalva of Arizona, and the liberal activist group MoveOn _ are now lining up behind her.

Sanders on Thursday night came closer that he ever has to acknowledging Clinton as the presumptive Democratic nominee, telling supporters he was ready to take on a role in trying to defeat Republican Donald Trump in November.

"The major political task that we face in the next five months is to make certain that Donald Trump is defeated and defeated badly," Sanders said during a live-streamed address to supporters. "And I personally intend to begin my role in that process in a very short period of time."

But he made no mention of rallying his supporters behind Clinton or releasing the delegates he's amassed over the long campaign. He said he and Clinton have "strong disagreements on some very important issues" even though they are close on others. Sanders also said he wanted to "transform" the party to ensure it focuses on the topics that were the foundation of his campaign for the nomination.

Rep. Peter Welch, a fellow Vermonter who endorsed Sanders in February, fretted that continuing his campaign could be counterproductive to Sanders' goal of securing policy and procedural commitments.

"Some believe _ and it appears this is Bernie's view _ that the longer he stays in, the more effective he'll be in negotiating. My view is that the sooner we get unified the better," Welch said on Thursday before Sanders spoke. "Bernie doesn't give up any leverage by acknowledging explicitly that Hillary will be the nominee."

Jim Manley, a former communications strategist for Senate Minority Leader Harry Reid, said Sanders risks "marginalizing" himself, in the campaign and upon returning to the Senate, if he doesn't accept that he has lost.

"He risks throwing it all away if he doesn't quickly endorse Hillary Clinton," Manley said. "He still thinks he's got a lot of leverage and every day that goes by he's losing it. They might've been more inclined to take some of his concerns more seriously than maybe they need to now."

Manley said it's unlikely the platform committee, which will be staffed largely by Clinton delegates, would be less inclined to take Sanders seriously "if they don't get an indication that he's going to be a team player in the end. That's not how it works."

Sanders was riding high after he won his sixth straight contest in Wisconsin on April 5. "If we can keep this up," he told supporters that night in a fundraising email, "we're going to shock them all and win this nomination." When he lost New York two weeks later, and a quartet of East Coast primaries the following week, the writing was on the wall. But Sanders remained defiant, insisting he would keep fighting and contest the July convention by attempting to flip superdelegates to his side.

Many Democrats found that strategy _ an anti-establishment insurgent trying to push party elites to overturn the will of the voters and depose the first woman to be a major-party nominee _ puzzling. And it went nowhere. Sanders campaign manager Jeff Weaver said Thursday on Bloomberg TV's "With All Due Respect" that there's no lobbying of superdelegates going on now and none planned for the future.

Clinton has moved on to the general election, focusing her fire on Trump and ignoring Sanders on the campaign trail, and more recently has begun to reshape the Democratic National Committee.

Clinton surrogates say the campaign has implored them, in conference calls and via talking points, to be cautious when talking about Sanders, fearful of alienating his supporters in the general election. There's good reason. Sanders supporters are torn on whether to back Clinton in the general election, according to a national Bloomberg Politics poll taken June 10-13. Fifty-five percent of likely voters identifying as Democrats and independents who supported Sanders in the primary said they intend to pull the lever for Clinton in November; 22 percent picked Trump and 18 percent preferred Libertarian Party nominee Gary Johnson.

J. Ann Selzer, who conducted the poll, said Clinton did "reasonably well" with Sanders voters. "She has to be concerned, however, that she loses 40 points to Trump and to Johnson combined. It's a signal that full coalescence has not yet been achieved."

Weaver said that Clinton and Sanders, along with their respective staffs, are negotiating a series of changes to the party that include policies in the platform and process reforms such as eliminating superdelegates and calling for more open primaries.

"It is best for the party" if Clinton reaches out to Sanders supporters by endorsing "tangible, concrete changes" to the Democratic Party, Weaver said. "We would like to get to a place where we could very actively support the nominee."

The divisions were months in the making. Sanders has painted Clinton as too cozy with Wall Street and too entrenched in the political establishment to make a meaningful difference. Many Sanders voters drawn to his calls for a "political revolution" believe Clinton represents the status quo. He has fed an impression among his supporters that the rules of the nominating contest were stacked against him from the start, accentuating the bitterness toward her.

"I don't know if Bernie supporters are going to vote for Hillary," 31-year-old Bako Nguasong said at Sanders' final rally in Washington, D.C. on June 9. "It may already be too late."

"She's definitely the lesser of two evils but I don't trust her. She's very conservative. I know Donald Trump is evil, he's a racist, he's a misogynist," said Nguasong, who hasn't decided what she'll do in the general election. But Clinton, she added, is "not for the people. She's about money."

Sanders has, notably, dialed back his public criticisms of Clinton in recent weeks.

He knows, as all of us know, that Hillary will be the nominee," said Welch. "I think he's earned the right to take some time to figure out when and how to make that announcement."

Some Democrats fear those wounds won't heal until Sanders urges his followers to support Clinton.

"It's clear Senator Sanders wants to show that his campaign was not for naught, that it impacted the party and he'll have organizing power moving forward," Ben LaBolt, national press secretary for President Barack Obama's re-election campaign, said in an email. "But he doesn't want to be the last guy at the party after the music has stopped playing _ he should quickly announce his wins and make clear to his supporters that the best way to secure progress is to ensure Donald Trump doesn't get any closer to the Oval Office than the Starbucks across the street."

Arit John contributed.