If these seem like distinctions without much meaning to critics — since even the least ambitious of these plans would require liberal Democratic majorities in Congress to pass — they’re all part of the contest between Sanders and Warren to be recognized in the Democratic primary as the lead champion for progressives. At the same time, the war over white papers has terrified moderate Democrats, who worry that a race to the left will damage the party’s chances of defeating President Donald Trump — even as it electrifies the base.

"This is exactly the primary we should be having,” said Alex Lawson, executive director of the advocacy group Social Security Works. “When candidates compete to release the boldest policies, everyone wins — except the billionaires.”

But the escalating ambition and price tag of the proposals has also been turned into ammunition for Sanders and Warren’s more moderate opponents, such as former Vice President Joe Biden, Sen. Amy Klobuchar, and South Bend, Indiana Mayor Pete Buttigieg.

“When candidates compete to release the boldest policies, everyone wins — except the billionaires.”

“The stakes of defeating Donald Trump and the assaults on our values he commits daily are too great for our primary to devolve into who can sacrifice our policy advantages in a general election the fastest,” said Biden spokesman Andrew Bates.

Warren and Sanders regularly both dismiss such criticism and argue that the dearth of big ideas is what caused the party to lose the White House to Trump in the first place.

From criminal justice to campaign finance to foreign affairs, the policy skirmishes between Sanders and Warren have touched on nearly every big topic in the primary and broadened the debate among Democrats. For instance, along with Sanders, several candidates endorsed the idea of a wealth tax or said they were open to it after Warren rolled out hers.

Sanders and Warren have largely avoided direct conflict on the campaign trail, and neither campaign provided a comment for this story. But the policy feuds speak to growing tension between the two candidates below the surface.

Sanders and Warren have also used the liberal plans to elevate their candidacies at critical moments in their campaigns. Warren kicked off the tit-for-tat when pundits were writing her off for dead at the beginning of the primary. She outflanked Sanders in the spring by outlining her student loan debt proposal and wealth tax. At the time, Sanders had said he would “substantially lower” or “eliminate” student debt, but hadn’t revealed a specific proposal. Likewise, Sanders had suggested a wealth tax as away to pay for Medicare for All in 2017 and expressed support for it in a 1997 book, but had no official plan.

Sanders, meanwhile, has used his plans to get to Warren’s left as she has slowly overtaken him in national and early-state polls. For instance, he has cast himself as the candidate with the “most comprehensive” climate change plan. Warren rolled out a green manufacturing plan and other climate proposals that together total about $3 trillion. Sanders’ “Green New Deal,” released in August, would invest $16.3 trillion.

Sanders’ allies argue that he was the original candidate who transformed the debate in the Democratic Party by popularizing Medicare for All, free college education and a $15 minimum wage in his 2016 campaign.

Warren’s supporters likewise say that she shifted the Overton window on student loan debt cancellation by calling to eliminate $640 billion of it in April. Sanders later responded with a plan to get rid of all $1.6 trillion of it. He also proposed canceling all medical debt. Then this past week, after Sanders called for universal school meals, Warren proposed forgiving K-12 student breakfast and lunch debt.

Even when the one-upmanship has flown under the radar, it has addressed issues that could be important to activists, labor unions, and elected officials being courted by the two candidates.

In his criminal justice policy, Sanders proposed that mandatory minimum sentences should be scrapped, whereas Warren suggested Congress should “reduce or eliminate” them. Sanders would also ban the use of facial recognition technology in law enforcement and put an immediate moratorium on “algorithmic assessments” — controversial tools used to predict how likely a defendant or incarcerated person will re-offend — until an audit is conducted. Warren would establish a task force to examine facial recognition and algorithms.

Even as some of the more moderate candidates criticize Sanders and Warren’s proposals as unrealistic and politically damaging, the jockeying between the two shows how much the Democratic Party has changed since 2016, when Sanders was the sole unabashed progressive in the race. In fact, left-wing activists and insiders see 2020 as the first presidential race in years featuring two bona fide progressives, creating a competition the likes of which they’ve never seen.

“It’s pretty exciting,” said Rebecca Katz, a New York-based progressive consultant. “What their campaigns are doing is they’re allowing people to have real, substantive discussions about very detailed progressive policies and discuss the merits and really dream big.”

The wealth tax is a telling example, said Roosevelt Institute fellow Mike Konczal. There is no divide among progressive leaders over whether to establish it; the only disagreement between Warren and Sanders is over how much to tax.

“In every policy world, there is a much more progressive vision than the status quo before it,” he said. But in this primary, Konczal added, “It’s moved at such a rapid pace it’s hard to keep track of. It’s sort of amazing."