One obvious theory is gender: Sanders is a man; Warren is held to a double standard and more easily attacked for evasiveness and dishonesty. Still, Biden, Buttigieg and Klobuchar—each of whom attacked Warren while treating Sanders with kid gloves—would be just as unhappy to lose to a man as to a woman. And when Biden and Buttigieg went after Warren, they risked blowback from voters who don’t like it when a man goes after a woman too harshly.

A stronger explanation is that Warren and Sanders sold themselves differently. Warren built her candidacy on her obsession with policy and mastery of detail. Her “I have a plan for that” mantra thrilled her college-educated throngs. Therefore, not having a plan for a massive overhaul of one-sixth of the national economy was an untenable exception. Once Warren accepted that she had no choice but to get into the health care details, she compounded the problem with a plan that alienated both moderates (for its enormous cost) and progressives (for delaying single-payer until the third year of her presidency).

Sanders, on the other hand, has a base of supporters who are not hung up on policy details, and in some cases, mock the very idea of them. The democratic-socialist hosts of the Chapo Trap House podcast wrote a best-selling book with the subtitle, “A Manifesto Against Logic, Facts and Reason.” Their more serious point was that facts and numbers are often wielded selectively and disingenuously by people trying to squelch socialistic ideas. When Sanders defiantly waves off an inconvenient data point pushed by a member of the hated corporate media, he gives his loyalists more reason to cheer.

Still, there is reason to believe that an attack on Sanders’ resistance to math would contain his rise. The Democratic Party has plenty of moderates who get nervous about overpromising and overreaching. Even Sanders’ best national poll, a 3-point lead within the margin of error in a CNN survey last week, shows the combined support of him and Warren to be 3 points less than the combined support of the four leading moderates: Biden, Buttigieg, Klobuchar and Mike Bloomberg. If Sanders can be shown to be unwilling to grapple with the finer points of policymaking, that would likely hamper his ability to forge a coalition beyond his initial democratic-socialist base, which would in turn prevent him from securing the nomination.

But a bigger shadow lurks over the Democratic field: the ghost of the Republican presidential campaign of 2016, when the candidates (like Jeb Bush) who attacked the outsider with the intense fan base lived to regret it. If you attack Sanders, and his democratic socialist platform, as mathematically challenged, you are not just attacking Sanders. You are attacking democratic socialism itself. And if you’re in a party with a young wave of democratic socialists as its newest and most unpredictable force, you risk disaster.

No one can say with certainty how many Sanders supporters would abandon the Democratic nominee if he lost the nomination. But we do know that his supporters are, on average, less loyal to the Democratic Party than voters who prefer other candidates. The Economist’s data guru G. Elliott Morris reported, based on two months of his operation’s polling toward the end of last year, that 87 percent of Sanders supporters would stick with the Democrats if he wasn’t the nominee. That’s a lot, but more than 90 percent of Biden, Buttigieg, Klobuchar and Warren supporters said they would vote for the Democrats this fall, no matter what. And just a few percentage points, if even that, could decide the presidency.

When Biden, Buttigieg and Klobuchar go after Warren, they suspect they’re hurting a rival without costing themselves a potential vote in November. With Sanders, the math isn’t as simple. Estimates of the number of Sanders 2016 primary voters who cast a ballot for Donald Trump range from 6 to 12 percent. That’s actually fewer than the estimates of Hillary Clinton ’08 primary voters who backed Republican nominee John McCain over Barack Obama. But unlike 2008, the Sanders defectors may have been enough to tip Pennsylvania, Michigan, Wisconsin and the presidency into the Republican column.

A Pew Research Center poll from last June found 14 percent of Democrats hold a “very positive” view of socialism. That hardcore 14 percent are the voters most likely to walk if Democrats conclude not just that they don’t want to nominate the lone democratic socialist in the presidential race, but also that his entire platform is an exercise in magical thinking. This is the Democratic establishment dilemma: It doesn’t want to be a democratic socialist party, yet it needs democratic socialist voters to retake the White House.

Republican presidential candidates found themselves in a similar pickle in 2016. They feared Trump was unelectable, but they didn’t want to anger his supporters by trashing him or his positions. By bowing to Trump and his devout fans, Republicans won the White House. Sanders makes a parallel argument today: that “excitement and energy” are needed to defeat Trump. One South Carolina elected official Dalhi Myers recently switched her support from Biden to Sanders on that logic. As the Associated Press reported, Myers, a member of the Richland County Council, “said she started to feel that Biden’s candidacy, while familiar and perhaps comfortable, wasn’t going to be enough to inspire the young voters whom she sees as necessary to a Democratic general election win.”

We can’t know today whether Sanders could blaze a Trump-like path to the White House. We do know that the Republican acquiescence to Trump in 2016 changed the complexion of the GOP, perhaps for a generation. How Democrats react to the rise of Sanders today may similarly determine what kind of party they are going to be.