Senate Republicans turned President Trump’s impeachment trial into a farcical exercise in partisan whitewashing. That leaves the job of canceling Trump’s reality show presidency to U.S. voters.

A heavy responsibility thus lies on Democratic caucus and primary voters as they start selecting their party’s nominee next week. If they make the wrong choice, it means four more years of Trump’s corrosive assaults on reason, democracy, and basic human decency. For many, the right choice will require setting aside their ideological druthers and picking the candidate most likely to beat Trump in the Electoral College.

It’s hard to know at this point which candidate is most electable. It’s easier to say who isn’t—and Sen. Bernie Sanders tops the list. Despite the devotion he inspires among young left-wing activists, the self-avowed socialist is too far outside the U.S. political mainstream to be considered anything but the longest of long shots against Trump.

Sanders is Democrats’ Jeremy Corbyn option, someone who offers ideological catharsis to America’s perennially disappointed left but who cannot unite a Democratic Party—or a country—that lies much closer to the political center.

A solid majority of Americans (55 percent) have a negative impression of socialism. Young people have moved left in recent years, but the country as a whole hasn’t. A New Center survey finds that 34 percent of Americans place themselves on the right of the political spectrum, 23 percent on the left and 43 percent at the center. New Gallup polls also confirm that America remains a moderate country that lists slightly to the center-right.

Democrats split down the middle, with 42 percent identifying with the center and 42 percent leaning left. Independents are much more moderate: 60 percent identify with the center, 22 percent with the right and 17 percent with the left.

The basic electoral math shows Democrats can’t beat Trump with liberal-left voters alone, especially in the older, less educated and diverse Midwest states that decided the 2016 election.

They will need a nominee who can make inroads among swing voters in those states: moderate and GOP-leaning independents, college educated suburbanites, and culturally conservative, blue collar whites.

For Sanders, however, the first stumbling block would be moderate Democrats. His palpable disdain for them is amplified by zealous supporters who excoriate centrist Democrats as “neoliberals” or “corporate Democrats,” presumably because they obstinately refuse to see it’s time for America to trade in free enterprise for socialism.

No wonder White House aides view Sanders as their dream opponent this fall. Trump lately has been disingenuously defending Sanders in tweets and claiming Democrats are scheming to cheat him out of the nomination again.

Sanders has laid out an ambitious—even utopian—agenda for toppling “capitalism” and massively expanding federal power to reengineer a more equal America from the top down. Unfortunately, his “unapologetically progressive” ideas create enormous vulnerabilities for Democrats.

Start with his controversial plan to force all Americans into a government health care monopoly. Sanders’ backers insist that Medicare for All is popular, but public support quickly dissipates once voters understand what it means. They strongly oppose being compelled to give up the private insurance plans they get from their jobs, as well as the substantial tax hikes entailed in moving everyone into a public program. For example, a recent poll of Democrats in Michigan found only 18 percent who said they’d be willing to pay as much as 10 percent more in taxes for Medicare for All.

And it will take a lot more than that to cover the plan’s stratospheric cost—estimates range from $32 to $40 trillion over 10 years. Sanders hasn’t specified how he’d finance it, other than promising the super-rich will pay the full freight. Not possible, says Rob Shapiro, a prominent Democratic economist. He calculates that Congress could raise income and payroll taxes by 50 percent, and double the corporate tax, and still not cover more than 60 to 74 percent of the cost of moving 228 million more Americans to the Medicare rolls.

Sanders’ spending ambitions don’t stop with single-payer. A partial list includes his Green New Deal proposal ($16 trillion over the next decade); as well as multi-trillion plans to build affordable housing; rebuild infrastructure; make tuition “free” at all public universities; pay off all $1.6 trillion in college student debt; and, create universal preschool.

“ Another major political liability is Sanders’ call for a ban on fracking. ”

Although the U.S. unemployment rate has dropped to its lowest level since 1969, Sanders also is pushing an unprecedented federal job guarantee for all Americans. Each job would cost taxpayers around $56,000 and would likely wreak havoc in labor markets as low-wage workers flock to make-work public jobs.

All told, Sanders’ plan would cost about $60 trillion over the next decade, doubling the size of the federal government. It’s hard to believe that U.S. voters, already leery of Washington, will support Sanders’ redistributive superstate—especially when they learn it will mean punishing taxes on everyone or crushing levels of public debt.

Another major political liability is Sanders’ call for a ban on fracking. That would shut down the remarkable shale energy boom that over the past decade has made the United States the world’s largest producer of natural gas and oil. It’s bad climate policy and bad politics.

Posturing against fracking might gain Sanders extra voters in deep-blue California and Northeast, but it would hurt him (and Democrats down ticket) in pivotal battleground states such as Pennsylvania, Ohio, New Mexico, and Colorado. Shale production has created tens of thousands of good, middle-class jobs for the very blue-collar workers Sanders claims to speak for, not to mention lowering fuel costs for U.S. manufacturers and households. “If a candidate comes into this state and tries to sell that policy (a fracking ban), they’re going to have a hard time winning,” says Pittsburgh Mayor Bill Peduto, a Democrat.

These examples hardly exhaust the list of political flanks a Sanders nomination would expose. His relentless business-bashing—the private sector is always the villain Sanders’ economic parables—and his quasi-pacifistic security and foreign policy outlook also would be hard sells to moderate Democrats, never mind swing voters.

In fairness, Bernie Sanders is everything Donald Trump is not: honest, decent, and principled.

Authentic he is, but all the authenticity in the world can’t make Sanders the pragmatic leader Democrats need to build a winning coalition in November. But it would make him the perfect foil for Donald Trump, Fox News, and Republicans eager to deflect accusations of political extremism back onto Democrats.