Former Colorado Gov. John Hickenlooper warned during Tuesday night's Democratic primary debate that "you might as well FedEx the election to Donald Trump” if the party adopts Bernie Sanders' "Medicare for All" plan, the so-called Green New Deal and other populist initiatives.

Hickenlooper's admonition came as Montana Gov. Steve Bullock and former Maryland Rep. John Delaney also seemingly sought to pump the brakes on the sweeping proposals from Sanders and Massachusetts Sen. Elizabeth Warren.

"The policies -- this notion that you're going to take private insurance away from 180 million Americans," Hickenlooper began. "The Green New Deal, making sure every American is guaranteed a government job if they want -- that is a disaster at the ballot box, you might as well FedEx the election to Donald Trump"

In an explosive moment minutes later, Warren, seemingly frustrated by the pushback, unloaded after Delaney also sounded notes of caution.

"I don't understand why anybody goes to all the trouble of running for president of the United States just to talk about what we really can't do and shouldn't fight for," Warren said, her voice raised.

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In response, Delaney Campaign Manager John Davis shot back in a statement.

“Senator Warren doesn’t know anything about John Delaney," Davis said. "John’s running on universal health care, creating a carbon tax and dividend that would make the United States the world’s policy leader, a $2 trillion dollar infrastructure plan and big bold plans to rebuild rural America and our cities.

"It’s not about mushy compromise, it’s about getting the policy details right and not running on just what’s the best slogan," Davis added.

Earlier this month, Hickenlooper took a shot at his fellow 2020 Democrats, suggesting that his fundraising numbers were lower than theirs because they promised "free stuff" to voters.

"The bottom line is, for a small campaign like us from... you know -- Colorado's about 6 million or a little less than 6 million people -- it's harder to raise money because we don't, we're not promising free health care or, you know... free tuition for everyone, to forgive student debt," he told MSNBC.

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In an interview with Fox News this month, Hickenlooper said most Americans wouldn't support major changes to the health care system.

“I would argue that 'Medicare-for-all' would require 150-180 million Americans to give up their insurance and some people hate their private insurance, but there’s well over half that every poll demonstrates they don’t want to give up their private insurance," he said. "So, I don’t see that happening, but I do believe in a public option."