Buttigieg, who had spent more time in Nevada than all but a handful of the other candidates, used his concession speech to warn against a "rush to nominate Sen. Sanders," casting him as a disaster in waiting for Democrats up and down the ballot.

"I believe the only way to truly deliver any of the progressive changes we care about is to be a nominee who actually gives a damn about the effect you are having, from the top of the ticket, on those crucial, front-line House and Senate Democrats running to win, who we need to win, to make sure our agenda is more than just words on a page," Buttigieg said.

In his remarks, Buttigieg also sought to cast himself as a pragmatic, yet ambitious, candidate capable of building the kind of coalition that Democrats will need to assemble if they hope to defeat Trump in the general election.

Sanders, he said, would prioritize ideological purity and pie-in-the-sky policy proposals, while doing nothing to remedy the country’s political divisions.

“That is the choice before us: We can prioritize either ideological purity or inclusive victory. We can either call people names online or we can call them into our movement. We can either tighten a narrow and hardcore base or open the tent to a new, broad, big-hearted American coalition,” Buttigieg said.

Sanders on Saturday won the Nevada caucuses in impressive fashion. As early results trickled in, he was carrying more than twice as much support as his nearest rival, Biden. The results will give Sanders a substantial lead in the race for delegates to the Democratic National Convention, and critical momentum ahead of South Carolina's primary on Feb. 29 and Super Tuesday on March 3.

Buttigieg cast Sanders, a self-identified democratic socialist, as deeply out of touch with a broad swath of Democratic primary voters — and of voters who will decide whether Trump gets a second term in November.

"Sen. Sanders sees capitalism as the root of all evil. He’d go beyond reform and reorder the economy in ways most Democrats, let alone most Americans, don’t support," Buttigieg said. "Sen. Sanders’s revolution has the tenor of combat, division and polarization, a vision where whoever wins the day, nothing will change the toxic tone of our politics."

Despite Sanders's rise in the polls in recent weeks, his opponents have not attacked him in any sustained way. None have run television advertisements critical of his positions, and interactions on the debate stage have mostly focused on his ability to pay for his signature "Medicare for All" proposal.

Earlier this week, most candidates took aim at former New York City Mayor Mike Bloomberg, welcoming the billionaire to his first presidential debate with a withering barrage of attacks. Sanders was left mostly unscathed, with the exceptions of an aside from Biden on Sanders's record on gun control and several shots from Buttigieg.

That is likely to change in the days and weeks to come, as Democrats sound the alarm over the prospect of running on a ticket led by Sanders. Democratic angst over the prospect of a Sanders nomination is rising, though no concerted effort to stop him or rally behind someone else has emerged.

Buttigieg hinted Saturday that the detente toward Sanders is at an end.

"We can prioritize either ideological purity or inclusive victory. We can either call people names online or we can call them into our movement. We can either tighten a narrow and hardcore base or open the tent to a new, broad, big-hearted American coalition," Buttigieg said Saturday. "This is our shot, our only shot, to beat Donald Trump. So I’m asking Americans to make sure we make the right choice."