Memo to Vice President Biden; Mayor Bloomberg; Mayor Buttigieg; Senator Klobuchar; and Senator Warren:

At the Las Vegas debate, each of you took aim at one another, often to withering effect. But with few exceptions, you declined to really challenge Senator Sanders. If you repeat this strategy at the South Carolina debate this week, you could hand the nomination to Sanders, likely dooming the Democratic Party – and the nation – to Trump and sweeping down-ballot Republican victories in November.

The reasons for this dire prediction are many, as we note below, but one is paramount: Bernie Sanders is a socialist, and the political toxicity of his self-selected brand cannot be overstated. As recent polling from Gallup shows, 53% of voters, including 51% of Independents, say they would not vote for “an otherwise well-qualified candidate for president” if that candidate is a socialist. That’s game over.

Senator Sanders seems aware of the problem. Lately, he’s argued that Republicans are the real socialists, since they provide corporate giveaways through tax breaks. He’s said that regular Americans have socialism already, in the form of Social Security and Medicare. He claims, without evidence, that socialism is so popular that it would bring out younger and low-propensity voters at unprecedented levels. And he has tried to append the meaningless modifier of “Democratic” to his “socialist” label.

But none of this will work. Senator Sanders has said it many times, including in past political debates: “I am a Socialist. Of course, I am a Socialist.” His attempts to redefine the term or parse the nuances of his socialism, which has run from his early near-Trotskyism to his latter-day Nordic style, will be utterly lost. What voters will know, after nearly one billion dollars of negative ads from Team Trump, is that Bernie Sanders and his Party have embraced socialism.

To be sure, Donald Trump will call any Democratic nominee a “socialist”. But if it’s one of you, that charge will not stick, because it will be an obvious lie. You are Democratic capitalists. Your words, ideas, and histories are clear on this point, and voters will know it. By contrast, if Trump’s opponent is, as his team fervently hopes, a proud socialist, he will make the entire election – for president and for every other office on the ballot – a referendum on socialism. That is a fight that Democrats cannot win.

In this campaign – and in his 50 years in public life – Bernie Sanders somehow has skated past any serious, sustained scrutiny of his ideas and his record. Yet those are so extreme – so far outside the mainstream – that they simply must not be ignored during the remaining fight for the 2020 nomination. Either you will air and debate them now, and deny Sanders the nomination, or they will come roaring out of the Trump machine in the fall, when they will prove fatal.

You are almost out of time—Sanders could take a nearly insurmountable delegate lead on Super Tuesday. We believe it is imperative that one of you emerge as the nominee, so we urge you to take the fight to him at the next debate. Beyond the policy critiques that have constituted most of your limited thrusts at Sanders so far, he has an incredible list of political vulnerabilities that would be easy to unpack, even within the debate’s time-limitations. Here are some things you could press him on:

His Stunningly Radical Political History

In the early 1980s, Sanders campaigned for candidates from the Socialist Workers Party.

The stated goal of the SWP was "the abolition of capitalism.”

That party called for “the destruction of the bourgeois state,” arguing such an act ‘is a necessary prerequisite for the conquest of state power by the working class.”

Sanders was twice an elector for an SWP candidate for president who once said that American soldiers should “take up their guns and shoot their officers.”

That candidate called for the abolition of the US military.

Even in Congress, Sanders proposed slashing the military budget by half.

His Outrageous Support for our Enemies

In the middle of the Iran hostage crisis, Sanders’ party “called for…’solidarity’ with the revolutionary regimes in Iran...” How is such an attack in the hands of Trump not disqualifying for many voters?

His Hopelessly Out of Touch Views on Taxes

On CNN last year, Sanders said that Americans would be “delighted to pay more in taxes” to fund his huge new programs. How can he propose a huge new tax increase without saying how much it would be?

His Preposterous Spending Plans

Experts estimate that Sanders’ major proposals would cost a staggering $60 trillion and would double the size of the government (while his tax plans fall $27 trillion short of paying for it). There’s a reason that, when pressed on the cost of his plans, Sanders simply refuses to answer, saying he actually has no idea and “no one does.”

His Party is Himself

Sanders is not a Democrat, yet he is asking Democrats to give him their nomination as President of the United States. How, exactly, has he earned that?

Sanders has called the Democratic Party “intellectually and spiritually bankrupt,” so it is no surprise that he routinely has declined the Democratic endorsement for Senate in VT.

In 2011, he suggested it might be a “good idea” to primary President Obama in 2012. He had brought up a potential primary challenge to Obama several times that summer.

After 2016, he worked on the committee to change the DNC rules and now has said (in Las Vegas) that he won’t follow those rules.

These and many other aspects of his record would offer Trump a deadly arsenal with which to savage Sanders and down-ballot Democrats. Sanders’ notion that he is the most “electable” among you is laughable on its face, which is why Republicans are campaigning for him. For every voter he “mobilizes” with his radicalism, he will turn out at least one for Trump. Negative partisanship is powerful when the candidates are extreme. Loyal Democrats like us would support Sanders, but too many others wouldn’t.

Yet, while 2020 opposition researchers may know about the Sanders record, Democratic voters do not. It is your responsibility to tell them. It is your job to make clear that the current front-runner for the nomination is a ticking time bomb. It is on you to ensure that at-risk Democratic House Members are not forced to flee from the Party’s standard-bearer, a near-impossible task, as many have said.

We have seen this movie before. While there is no moral equivalence between Donald Trump and Bernie Sanders (none whatsoever), there is similarity between this moment and the 2016 Republican race. When Chris Christie took on Marco Rubio in their debate, it mortally wounded both candidacies and gave Trump a clear path to the nomination.

We understand that you want to be the only Sanders alternative left standing. We appreciate the collective action problem. We know his supporters defend him with hostility and bile. But the moment calls for rising above those concerns. Pick an issue and hammer him on it. Act for yourself, your party, and your country. The political imperative of our time is saving the republic from the catastrophe of a Trump second term. To do so, it is vital that you take on Bernie Sanders and that you do it NOW.