Senator Bernie Sanders’s presidential candidacy poses a conundrum for progressives. Not since 1936, when Franklin Roosevelt said that he “welcomed” the hatred of corporate interests, has a serious presidential candidate offered so aggressive a challenge to the conservative powers that be. At the same time, however, a dangerous lunatic is president of the United States, and Sanders, of all the major Democratic contenders, is the one who will make Donald Trump’s reelection most likely. Eight years of a Trump presidency could mean the end of meaningful democracy in the United States, along with many of the rights that women, minorities, immigrants, LGBTQ people, and others now take for granted.

Let me clarify: I’ve been a fan and supporter of Sanders ever since he was elected mayor of Burlington, Vermont, in 1981. I was honored to be asked to testify before him in Congress years ago, and I voted for him in the New York presidential primary in 2016. I did so, however, not because I imagined he might win the nomination, but because I hoped that a strong showing by Sanders would help wake up Hillary Clinton to the importance of addressing economic inequality, and also to honor his brave criticism of Israel’s occupation of the West Bank.

I was wrong. Sanders turned so negative toward Clinton that it hurt her in the general election. Even though he campaigned for her after he lost the nomination, roughly 12 percent of Sanders’s supporters switched to Trump, and enough of the rest supported Jill Stein’s kamikaze candidacy that it helped tip key states to Trump.

Sanders has now hired two press aides, David Sirota and Briahna Joy Gray. The former had recently devoted himself to harsh Twitter attacks on Sanders’s potential rivals for the nomination. (Sirota has since deleted his Twitter archives.) The latter, also a frequent and combative tweeter, ended up a Stein supporter in 2016. Their hires appear to presage a take-no-prisoners campaign that could conceivably put Sanders over the top in the primary while also alienating most of the electorate.

In a poll of likely primary voters in the battleground state of Wisconsin, Sanders crushed the field with a 40 percent showing. But he already has a 45 percent unfavorable rating among all voters, up from 36 percent three years ago. His favorable number is down to 46 percent, 13 points lower than it used to be. And this is before the Trump/Fox News/Breitbart/Facebook/Twitter/YouTube right-wing noise machine turns its poisonous attention to him—to say nothing of Wall Street and all the other industries that will no doubt strenuously oppose him.

Sanders today insists on calling himself a “socialist,” but he no longer holds most of the positions historically associated with socialism. He should know this because he was a serious socialist between 1972 and 1976, when he ran and lost in four statewide Vermont races on the Liberty Union Party line. His platform called for the nationalization of pretty much every industry in America, together with a 100 percent income tax on America’s top earners. And Sanders was still a socialist in 1980, when he served as an elector for the Trotskyist Socialist Workers Party, which favored the abolition of the US military budget and proclaimed itself in solidarity with both Cuba and Iran at a time when the latter held over 52 Americans hostage.

I held some of the same views myself as a young man, but I am not running for president. And if I ever thought I might, I probably wouldn’t have agreed to attend a rally in 1985 in Managua, Nicaragua, with a crowd chanting, “Here, there, everywhere, the Yankee will die,” while the Nicaraguan president, Daniel Ortega, condemned my country’s “state terrorism” (accurate as the term was).

I mention this appearance because, according to reporting by journalist Kurt Eichenwald, Republicans have it and similar events on tape. They also have binders full of statements made in support of the kind of socialism that Sanders backed before he became what he is today: a typical New Deal–style liberal or European social democrat. Much of Sanders’s agenda is popular, but calling yourself a “socialist” is, according to recent polls, a losing proposition—74 percent of independent voters disapprove of it, with just 9 percent approving.

Sanders consistently speaks of the “political revolution” that he expects will carry his campaign across the finish line. He is, however, a candidate with views that, like mine, are to the left of the American “center,” wherever that may be. He is also a candidate who will be 79 years old in January 2021; who refuses (thus far) to release his tax returns and thereby robs the Democrats of a potent weapon against Trump; and who cannot even bring himself to become a member of the party whose presidential nomination he seeks. (Insert Groucho Marx joke here.) And I’ve not even mentioned his weakness, relative to Clinton, with crucial Democratic constituencies like African Americans and women. We can also count out the many voters who are uncomfortable with criticism of Israel (much as I admire Sanders for that).

A Sanders nomination would, I fear, deliver the country to Trump. It would depress turnout among all the groups I mentioned; increase support for the likely spoiler in the race, Starbucks CEO Howard Schultz; and keep a significant number of swing voters in Trump’s column. Additionally, some of the moms and grandmas who make up the backbone of the #Resistance told researcher Theda Skocpol that, owing to Sanders’s harsh treatment of Clinton in the 2016 election, they might sit out 2020 if he’s the nominee.

Someday, all of this may change, and I—or more likely my daughter—will be able to vote for Alexandria Ocasio-Cortez for president. Today, however, with Trump as president, Democrats cannot afford to bet America’s future on an invisible “revolution.” Here’s hoping they realize this soon enough to protect the progressive achievements of the past from the destruction and devastation that would be the inevitable result of four more years of Donald Trump.