Joe Biden is trying to turn a wave of sudden momentum, achieved in South Carolina, into a wider breakthrough in the Democratic race. (File)

Written by Alexander Burns, Jonathan Martin and Nick Corasaniti

In a last-minute bid to unite the moderate wing of the Democratic Party, Sen. Amy Klobuchar and Pete Buttigieg on Monday threw their support behind a presidential campaign rival, Joe Biden, giving him an extraordinary boost before the Super Tuesday primaries that promised to test his strength against the liberal front-runner, Sen. Bernie Sanders.

Even by the standards of the tumultuous 2020 campaign, the dual endorsement from Klobuchar and Buttigieg — and their plan to join Biden at a rally in Dallas on Monday night — was remarkable. Rarely, if ever, have opponents joined forces so dramatically and swiftly, as Klobuchar and Buttigieg went from campaigning at full tilt in the South Carolina primary Saturday to teaming up on a political rescue mission for a former competitor, Biden, who they had once regarded as a spent force.

Klobuchar, who sought to appeal to the same moderate voters as Biden and Buttigieg, and focused her campaign on calling the Democratic Party’s attention to Midwestern states like her native Minnesota, withdrew from the race Monday afternoon after intensive conversations with her aides following Biden’s thumping victory in South Carolina.

Rather than delivering a traditional concession speech, Klobuchar told associates she wanted to leverage her exit to help Biden and headed directly for the joint rally.

For the three moderates, as well as for Sanders and other remaining candidates, the crucial question hanging over the fast-moving events was whether any of it would make a difference in Tuesday’s primaries across 15 states and territories, including the critical battlegrounds of California and Texas. Millions of voters are expected to go to the polls, but many states have had early voting underway; more than 2.3 million Democratic and independent ballots have already been processed in California.

Sanders has significant head starts in many of the Super Tuesday states and beyond: His popularity has risen in recent weeks, and so has Democratic voters’ estimation of his electability in a race with President Donald Trump. The Vermont senator has a muscular national grassroots organization, backed by the most fearsome online fundraising machine in Democratic politics — one that collected more than $46 million last month, far outdistancing every other candidate in the race.

Sanders signaled Monday that he was ready for a fight against Biden, and perhaps a long one, if neither man can achieve a decisive early advantage in a nomination fight that still includes Sen. Elizabeth Warren of Massachusetts and Michael Bloomberg, a billionaire former mayor of New York City. Sanders’ advisers have long believed that he would have an advantage in a two-person contest against Biden, because of the strength of Sanders’ economic platform and message of shaking up the political system.

And Sanders’ supporters are unlikely to be impressed by movement toward Biden among traditional Democratic power brokers, who many Sanders voters already regard as having colluded in an unseemly way to block his candidacy in 2016. There is some risk to party leaders that anything perceived as a conspiracy against Sanders could anger his base and deepen existing fissures on the left.

As news emerged of the shift of centrist support toward Biden, Sanders projected confidence and defiance, dismissing it as a phenomenon of “establishment politicians” supporting one another. On Twitter, Sanders posted a video criticizing Biden for having supported the 2003 invasion of Iraq, linking him to unpopular Republicans like former President George W. Bush and former Vice President Dick Cheney.

“I do not believe we will defeat Donald Trump with a candidate like Joe Biden who supported the Iraq War,” Sanders wrote.

That Klobuchar and Buttigieg decided to align against Sanders reflected their assessments of him as a general election candidate: Both have warned he could lose to Trump, skeptical that his liberal policy agenda would win him broad support in battleground regions like their Midwestern base.

But the one-two punch also involved their own political interests, since leaving the race spared Buttigieg and Klobuchar the possibility of a wilting finish Tuesday.

Klobuchar’s exit came a day after Buttigieg’s, though he did not immediately issue an endorsement as she did. The former mayor of South Bend, Indiana, won the Iowa caucuses barely a month ago by the narrowest of margins and finished a close second to Sanders in New Hampshire. Both Buttigieg and Klobuchar failed to find a substantial constituency in the larger and more diverse states that have only now begun to hold primary elections.

Klobuchar spoke briefly Sunday with Biden at the commemoration of the civil rights march in Selma, Alabama, but they did not discuss the possibility that she would end her campaign, a person briefed on the conversation said. And Klobuchar made her final decision Monday morning without speaking again with Biden.

It is not uncommon for former presidential rivals to endorse each other later in an election season: The vanquished John Edwards helped Barack Obama conquer Hillary Clinton in 2008, for instance, and in the 2016 Republican primaries, Trump earned a crucial seal of approval from an adversary he had handily trounced, Chris Christie.

In that 2016 race, some Republican leaders wanted other candidates to drop out early and unite behind one stop-Trump contender; that never happened, as Sen. Ted Cruz of Texas, Sen. Marco Rubio of Florida, Gov. John Kasich of Ohio and Ben Carson all competed on Super Tuesday that year against Trump, who came out ahead in states and delegates.

Together, the moves by Klobuchar and Buttigieg — who nursed their own bitter rivalry for much of the primary campaign — amounted to an urgent and perhaps desperate effort to strengthen Biden in the first nationalized day of voting in the Democratic nomination contest. Super Tuesday includes the largest states in the country, California and Texas, and a number of important general election swing states, including Virginia, North Carolina and Klobuchar’s own Minnesota.

Biden is trying to turn a wave of sudden momentum, achieved in South Carolina, into a wider breakthrough in the Democratic race, having slumped badly over the last few months after embarrassing setbacks in the first three primary and caucus states. Even with his former opponents’ energetic help, Biden is by no means certain to run strong enough Tuesday to slow Sanders’ ascent or narrow the race to a one-on-one contest.

Ari Rabin-Havt, Sanders’ deputy campaign manager, told reporters Monday that the campaign was untroubled by the recent developments and that it did not intend to change its strategy. The campaign announced over the weekend that it was starting a new wave of advertising in states that vote on Super Tuesday or later, including big battlegrounds like Florida, Michigan and Arizona.

“Watching the campaign, watching the 10 debates unfold, we believe they have constantly shown that Bernie is the strongest candidate to defeat Donald Trump, and that’s still the case,” Rabin-Havt said. “And we think we still are in a very strong position heading into Super Tuesday.”

There were a few signs of frustration from Sanders’ camp, most significantly when Harry Reid, a former Senate majority leader from Nevada, issued an endorsement of Biden. The announcement prompted a tart reaction from Faiz Shakir, Sanders’ campaign manager and a former aide to Reid, who tweeted that it was “disappointing.”

“I’ll forever have respect and love for Sen. Reid,” Shakir said. “But I’m old enough to remember when he thought Biden’s ideas were worthy of being put in a fireplace.”

Democratic officials say that Reid has been helpful in rallying support behind Biden, and has quietly talked to a handful of the now-former candidates. In a telephone interview Monday night, Reid acknowledged speaking with Klobuchar earlier in the day, before she dropped out. And while he insisted she was already planning to withdraw from the race when they talked, Reid acknowledged he has been working behind the scenes.

“I do my best,” he said. “We need less confusion about who we’re all for.”

So far, Sanders has made few concessions, or even gestures of conciliation, toward the Democratic Party establishment he is aiming to displace, and if Biden does manage to slow or halt his ascent Tuesday, it could be seen in part as a function of just how little Sanders has done to assuage moderates’ anxiety about his campaign.

After a triumphant win in the Nevada caucuses late last month, Sanders delivered a victory speech in Texas that sounded like a plea for unity. But he then spent much of the next week defending his own provocative pronouncements, including his past praise for the Cuban government, and making a doomed attempt to undercut Biden in his stronghold of South Carolina. And he spent valuable time campaigning in Warren’s Massachusetts and Klobuchar’s Minnesota to try to beat them on their home turf — a gamble that could have unpredictable consequences, given Klobuchar’s decision to leave the race.

Warren has shown no sign of yielding to Sanders, and Monday she collected an endorsement from Emily’s List, the national Democratic women’s group. Her campaign has laid out a plan to amass delegates, state by state, until the nomination is decided at a contested convention — a risky strategy, and one that could significantly complicate Sanders’ hopes of building a rock-solid coalition of support on the left.

Over the weekend, Klobuchar’s political allies were split about whether she should press on, with some arguing that she should compete through Tuesday because she would probably carry Minnesota and deny Sanders the opportunity to harvest a large number of delegates there. In her own internal polling, Klobuchar held a 13-point lead over Sanders, who was in second place with a narrow lead over Biden, according to a copy of the poll reviewed by The Times.

But after Biden bested Sanders in South Carolina by nearly 29 percentage points — and outdistancing Klobuchar and Buttigieg by an even more towering margin — Klobuchar began to deliberate with her advisers about whether it made sense to continue in the race even until Tuesday, according to people familiar with the conversations, who spoke on the condition of anonymity.

The decision caught some of her staff by surprise, coming even as members of her team were in the process of buying airtime for future television ads. At a Salt Lake City rally Monday morning, Klobuchar betrayed no indication that she was about to end her candidacy.

With her abrupt withdrawal, Klobuchar believes there is at least some chance that Minnesota could tip toward Biden. On a phone call with her staff, she said she was proud of having run a “happy, happy campaign.”

Klobuchar said on the call that she had to consider “what is best for our country right now,” explaining that had led her to support Biden.