The Democratic Party's anti-Sanders crusade switched into high gear Monday, on the eve of the most critical day in the presidential primary season.

Two of the highest profile Democratic contenders, Amy Klobuchar and Pete Buttigieg, ended their presidential bids within a day of each other and moved instantly to endorse Joe Biden.

For weeks, candidates have refused to coalesce around a clear alternative to socialist Bernie Sanders, even though they and the party have been aghast and increasingly alarmed by his march toward victory. But now, they have finally snapped into crisis management mode in hopes of preventing him from collecting a motherlode of Super Tuesday delegates.

There are 1,357 delegates at stake in the 14 Super Tuesday states — Alabama, Arkansas, California, Colorado, Maine, Massachusetts, Minnesota, North Carolina, Oklahoma, Tennessee, Texas, Utah, Vermont, and Virginia, along with Democrats abroad, and caucuses in American Samoa.

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Buttigieg, the former South Bend, Indiana, mayor, and Klobuchar, a Minnesota senator, dropped out after single-digit finishes in Saturday's South Carolina primary. Each is expected to announce endorsements for the former vice president at a Biden rally in Dallas on Monday evening.

Candidates and analysts warned that Sanders, a socialist Vermont senator, is slated to gain a large lead in delegates on Super Tuesday that would be nearly impossible to stop with Klobuchar, Buttigieg, Biden, and former New York Mayor Michael Bloomberg splintering support among centrist voters.

After failing to gain traction for their own candidacies by attacking Sanders in last week's debate, the candidates took action beyond vague warnings of Sanders endangering Democratic White House hope in acts of self-sacrifice.

Buttigieg, in his drop-out speech, warned against making a left-wing ideologue the party's nominee, reiterating one of his main messages from the last few weeks of his campaign.

"We need a broad-based agenda that can truly deliver for the American people, not one that gets lost in ideology," Buttigieg said Sunday. "I urge everyone who supported me to continue in the cause of ensuring that we bring change to the White House and working to win the absolutely critical down-ballot races playing out across the country this year."

Bloomberg is now the only centrist other than Biden left in the race, but his capacity to spend his $56 billion fortune on his bid was not enough to keep Buttigieg and Klobuchar from waiting to endorse a candidate or endorsing him instead — particularly after two stiff debate performances in Nevada and South Carolina. The threat of Sanders, it seems, is too big to wait until after a third of nominating delegates are allocated in March 3 Super Tuesday contests.

Former Senate Majority Leader Harry Reid, who declined to endorse a candidate before the Feb. 22 caucuses in his home state of Nevada, also endorsed Biden on Monday.

"Joe Biden’s strength of character and deep experience stand in the starkest contrast to Trump’s amorality, corruption and utter incompetence,” the Nevada Democrat said in a statement.

His endorsement, along with a wave of other elected officials that Biden's nearly 30-point win the South Carolina primary, cements Biden as the clear establishment and centrist-favorite alternative to Bernie Sanders.

Illinois Sen. Tammy Duckworth, former Virginia Gov. Terry McAuliffe, former Democratic National Committee chairwoman and Florida Rep. Debbie Wasserman Schultz, and several other members of Congress endorsed Biden following his win in South Carolina.

With candidate drop-outs and subsequent endorsements, Biden is finally evolving from a fragile and flailing front-runner to running the campaign that his team wanted all along: the clear, normal, experienced candidate who is good enough to represent the majority of Democrats across ideologies in a fight against President Trump.

Several other former Democratic presidential candidates have endorsed Biden: Former Maryland Rep. John Delaney, Massachusetts Rep. Seth Moulton, and Ohio Rep. Tim Ryan.