The senator from Vermont is Hillary Clinton’s rival in the contest for the Democratic presidential nomination.

The senator from Vermont is Hillary Clinton’s rival in the contest for the Democratic presidential nomination.

The senator from Vermont is Hillary Clinton’s rival in the contest for the Democratic presidential nomination.

During a fiery speech to supporters late Tuesday night in California, Bernie Sanders rattled off several reasons why he’s staying in the race against Hillary Clinton. But there was strikingly little said about what typically would be the most compelling one: winning the Democratic nomination.

The senator from Vermont drew deafening cheers from the crowd of more than 3,000 in Santa Monica when he said he would make good on his promise to fight for every vote, including in the final primary Tuesday in the District.

And his followers screamed in appreciation when Sanders talked about the issues he still plans to press, including breaking up the big banks and making health care a universal right.

But the reality of a long day in which Sanders lost decisively to Clinton in California — where he had hoped to score a statement-making upset — appeared to be sinking in.

“I am pretty good in arithmetic, and I know that the fight in front of us is a very, very steep fight,” the self-described democratic socialist told his supporters. “But we will continue to fight for every vote and every delegate we can get.”

Despite Hillary Clinton’s delegate gains on Tuesday, presidential candidate Bernie Sanders promised to “continue to fight for every vote and every delegate,” until the Democratic convention. He also slammed GOP rival Donald Trump as “a candidate whose major theme is bigotry.” (Jenny Starrs/The Washington Post)

The reality is, what for weeks had already been a “narrow path” for Sanders to catch Clinton in the delegate chase had turned into the remotest of possibilities.

[‘We’ve reached a milestone:’ Clinton claims the nomination]

With Tuesday’s results, Clinton extended her lead in pledged delegates — those won in primaries and caucuses — to 375, the largest it has been since the primary season began, and far larger than Clinton ever trailed now-President Obama during the 2008 election, according to a preliminary tally by the Associated Press.

The margin is likely to grow by next week after the primary in the nation’s capital, where Clinton is heavily favored.

That means that Sanders’s only remaining path to the nomination is persuading hundreds of the superdelegates who have announced their support for Clinton to switch sides before the Democratic convention in July. And the superdelegates — elected officials and party elites free to support their choice for president — have so far been presented with few compelling reasons to do so.

A close look at the math should be particularly sobering for Sanders and his supporters.

On the night six states including California and New Jersey went to the polls, Sen. Bernie Sanders (I-Vt.) vowed to continue "the struggle," even as rival Democratic presidential candidate Hillary Clinton had pivoted to thanking supporters and slamming Republican Donald Trump. (Sarah Parnass/The Washington Post)

As of Wednesday, Clinton’s combined delegate count — pledged delegates and superdelegates — stood at 2,777, or 394 more than she needed to clinch the nomination.

That means that to catch her, Sanders would have to persuade more than two-thirds of the 574 superdelegates who have already announced for Clinton to abandon her and join his cause.

And he is asking them to do it at the end of a nomination process in which Clinton has won more states, more pledged delegates, more superdelegates and more overall votes than Sanders.

Clinton has run stronger in the party’s primaries, which attract more voters, while Sanders has shown more strength in caucuses, in which a smaller group of more devoted followers tend to participate. And Clinton has tended to do better in the bigger, more racially diverse states than Sanders, who struggled from the outset to connect with African American voters.

Sanders has also won fewer states and fewer votes than Clinton did during her failed primary campaign against Obama in 2008.

[Next for Democrats: A delicate dance to broker peace between Clinton and Sanders]

During his Tuesday night speech, Sanders recalled that he had initially been written off as a “fringe” candidate and that his campaign had proven the pundits wrong. He has run a spirited race and given Clinton a far stiffer challenge than her campaign ever envisioned.

For some time now, though, Sanders’s rationale for staying in the race has been evolving.

More than a month ago, he summoned reporters to Washington and said that he expected to go on a run in the final stretch of the primary season and had a reasonable shot at catching Clinton in the pledged delegate count.

That was among the reasons Sanders said superdelegates should consider backing him — because he would be the candidate with momentum. That argument vanished after Tuesday’s defeats in California and New Jersey, another delegate-rich state, and a decisive loss in Puerto Rico over the weekend.

Sanders has also argued — and continues to make the case — that he would be a stronger candidate than Clinton in the fall election against Republican presumptive nominee Donald Trump. That is based on a series of polls that generally have shown him winning by more than Clinton.

Clinton partisans counter that Sanders has never been on the receiving end of a national negative ad campaign, and that those numbers would probably change as soon as that happened.

Sanders also touts his strength with independent voters as an asset for the fall, as well as his far greater appeal than Clinton among young voters. He tends not to mention that Clinton has done comparably well with older voters.

One constant in Sanders’s drive toward the finish line is his belief, aides say, that the more delegates he accumulates, the more influence he will have over the Democratic Party platform.

Sanders has made income inequality a rallying cry during his campaign, and most of the related issues he champions are the same ones he has pushed for decades in his congressional career.

During the campaign, he has seemingly pushed Clinton to her left on several issues, including trade policy and Wall Street reform.

And Sanders has already secured an unusual number of seats on the committee that will draft the Democratic platform, which met for the first time Wednesday. Sanders has indicated he wants to push the party on a range of issues, including support for a $15 minimum wage and a more “balanced” policy toward the Middle East.

Sanders is also seeking to open more primaries and caucuses to independent voters and has said he would like to see the influence of superdelegates curtailed in future elections.

Several weeks ago, as Sanders was asked about his staying power in the race, he said that it would be “undemocratic” to bow out before every voter in the Democratic primaries and caucuses had a chance to express their preference.

With his decision to contest the District primary next week, Sanders is staying true to his view.

His campaign announced plans Wednesday for a large-scale rally on Thursday night at RFK Stadium in Washington.