ANALYSIS/OPINION:

LOS ANGELES — The acrid odor of Democratic panic, as real as the aroma of burned flesh and cordite on a battlefield, hangs over California in a dark cloud of confusion and uncertainty. “This is how it smelled in ‘64,” says a stunned Democratic observer in Sacramento, “with [Barry] Goldwater charging and [Nelson] Rockefeller on the run.”

This time Hillary Clinton has the Rockefeller role, with Bernie Sanders in passionate pursuit as the stand-in Barry Goldwater. The point is that suddenly the Democratic world is about to be turned upside down, and everyone is plundering precedents to make sense of it. Only weeks ago Hillary was so far ahead — leading by up to 60 points in some public-opinion polls — that the notion than Bernie could catch her was mere fantasy.

A new Wall Street Journal-NBC News poll, conducted by Marist, demonstrates the impossible, on the crucial weekend before the Tuesday vote, that the race is statistically tied, with Hillary leading by only 2 points, 49 percent to 47 percent among most likely voters. From so far behind that he might as well have been campaigning in New Zealand, the 74-year-old Socialist Santa Claus from the kingdom of free stuff has pulled even and surges for the finish with the momentum.

Hillary is still the way to bet, if bet a man must. She has the committed delegates, she has the superdelegates and she has the party machinery pulling out the stops. What she doesn’t have is the fire and passion of the momentum heading into the all-important final weekend of the campaign. Momentum — “the big ‘Mo,” George Bush the Elder called it — nearly always awards the victory to the candidate who has it at the finish.

Winning California, important as it is, is not necessarily decisive in November. Barack Obama lost California to Hillary eight years ago and won the nomination, and the election. But Hillary cannot afford to lose on Tuesday. Even winning by squeezing out a close victory would sharply disappoint. She needs fewer than 50 delegates to seal a success, and 600 delegates will be in play on Tuesday. A loss here would be, if not catastrophic, at least disastrous.

Momentum dispenses its own rewards. Donald Trump, who never lets an occasion go by without butting in and if there’s no occasion he will make one, has been mocking Hillary’s inability to close with strength. This week, as if to make the Donald’s point, the Clintons, Bubba and wife, deserted the campaign in four other states — New Jersey (51 delegates), South Dakota (29), Montana (27) and New Mexico (24) — to put all their resources here. They’ve cleared out everything for 30 events between now and Tuesday.

“[Bernie] has been out there for three weeks solid,” says Bubba, the master playing defense, “and we’ve been campaigning in all the other states. California has been good to us, to Hillary particularly. Eight years ago she did very well. I think it’s really a question of turnout.”

It’s the surge of the newly registered, unaffiliated voters who have the Clintons on edge. Mr. Sanders has done very well with the independents, and a big part of his campaign has been a successful appeal to voters who have rarely voted in primaries.

This has been a week for gallantry in the ranks of a party that puts small value on such old-fashioned notions, with three important men coming to the aid of the lady in distress. President Obama gave her the endorsement that looked for a long time he was saving for someone else. This week Jerry Brown, the governor who finally outran a reputation as Governor Moonbeam, endorsed her, but it sounded only like an endorsement of the last man (or woman) standing who could block Donald Trump’s road to Pennsylvania Avenue. And of course Bubba, always Bubba, trying to make good his end of the pact the two of them made at Yale in a previous century: “You help me get to the White House, and then I’ll help you follow me.”

The harsh reality, that she needs a barn-burning finish to save her presidential campaign, illustrates the pinch Hillary finds herself in, and suggests that she will struggle mightily against Donald Trump. The Donald’s party rivals are quickly falling into line. Paul Ryan tipped his hat to the inevitable Thursday.

If Bernie defeats her on Tuesday, all bets on the Philadelphia convention next month are off. The superdelegates could stampede to somebody, perhaps Bernie but more likely Joe Biden, and deliver what everybody has been hankering for, an open convention. Ain’t we got fun?

• Wesley Pruden is editor in chief emeritus of The Times.