Is Senator Bernie Sanders (D-Vt.) electable? As Sanders has surged in the polls, supporters of former Secretary of State Hillary Clinton are issuing increasingly dire warnings about his general election prospects. On websites like Vox, many political scientists agree: He can’t win. Millions of dollars in Republican ads, they insist, will paint him a socialist or a red. Americans aren’t about to elect a Jewish socialist who still hasn’t lost his Brooklyn accent.

It will be a debacle, critics predict, like Democratic Senator George McGovern’s crushing 1972 loss, when the Democrats lost 48 states, or Republican Senator Barry Goldwater, buried by President Lyndon B. Johnson’s stunning landslide in 1964. It will set progressives back for decades.

Ironically, as Sanders rises in the polls and does better than expected, the alarms grow in volume and intensity. It verges on oxymoronic for Clinton and the party establishment to scorn as unelectable a candidate who is beating her at the ballot box.

Insurgent candidates face forbidding odds — but they don’t always lose. In 1980, establishment Republicans issued much the same warnings about former California Governor Ronald Reagan, asserting he would be Goldwater redux. Moderate Republican John Anderson went so far as to mount a third party bid against him.

Reagan not only won, he led a re-alignment election. Republicans took control of the Senate, and launched, in Barack Obama’s words, a transformative presidency that marked the end of the New Deal coalition and the beginning of the conservative era. (In 1984, Walter Mondale lost 49 states to incumbent President Reagan).

President Richard M. Nixon and then Reagan built the conservative Republican majority coalition by splitting off so-called Reagan Democrats — largely white, disproportionately Southern, working-class men — from the Democratic Party. The GOP attracted these voters with talk of God, guns and skillful use of race-baiting politics, while waging a culture war against gays and women.

Sanders similarly may have the potential to expand the Democratic majority coalition by attracting blue-collar, white male voters back into the Democratic Party.

As Donald Trump’s rise in the 2016 Republican primaries has shown, these blue-collar white male voters are restive. Trump has garnered significant support with anti-immigrant and anti-Muslim diatribes. But he’s also echoed Sanders by scorning the corruption of U.S. electoral politics, failed U.S. trade policies and endless wars without victory.

Sanders’s passionate populism may gain him a hearing from these voters and potentially forge a far broader electoral majority coalition for Democrats.

Predicting whether Sanders is a Reagan or a Goldwater isn’t easy. Polls that show him doing well in match-ups against potential Republican nominees are virtually meaningless. Sanders hasn’t even introduced himself to most Americans and the Republican assault on him hasn’t begun.

The assumption that he wins the nomination — against Clinton, who enjoys universal name recognition, the support of virtually the entire Democratic establishment, the best party operatives and all the money in the world — posits a stunning political rise. It would mean that Sanders makes significant inroads among minority voters, sustains the enthusiasm of the young and consolidates his support among middle- and lower-income Democrats.

As Alan Abramowitz, a political scientist from Emory University, has wisely noted, the fears of a Sanders electoral debacle may be overdone simply because the electorate is far more polarized now than when McGovern and Goldwater ran. The harsh negative partisanship of U.S. politics, the growth of segmented media and the rise of social media have all helped consolidate more ideologically cohesive voting blocks.

A Clinton candidacy, for example, will mobilize the Republican right, which loathes her nearly as much as they do Obama. The Republican nominee is most likely to push an extreme right-wing agenda that will help unify and mobilize the Democratic base, no matter who the Democratic nominee is.

The question of electability is generally a comparative one: Is Sanders more or less electable than Clinton? There’s a natural tendency to assume that Clinton, the more moderate and experienced candidate, is presumptively more viable. But while Sanders has clear vulnerabilities, so does Clinton. She is burdened with significant baggage — Wall Street money, the smarmy Clinton Foundation fundraising, the email mess and more. Sanders has been the most courtly of opponents, but Republican attacks are and will be incessant and poisonous. Polls indicate Clinton already faces troubling doubts about her honesty.

Democrats go into the 2016 election cycle confident that they have a majority coalition: the young, people of color, unmarried women, and liberal professionals. If they show up in large numbers at the polls. Already, polls report an alarming “enthusiasm gap” between Democratic and Republican voters. Sanders has clearly electrified young people, whereas Clinton has not. Sanders won voters aged 17 to 29 by an astounding 84 percent to 14 percent in Iowa, and he enjoys a similar margin in tracking polls in New Hampshire.

This is a troubling time, particularly for this new Democratic majority. The nation is still struggling to recover from what Nobel Prize-winning economist Joseph Stiglitz has begun calling the “long depression.” Young people find themselves burdened with college debt, struggling with lousy job opportunities, inheriting a world of ceaseless war and catastrophic climate change. With wages stagnant and jobs insecure, Americans fear losing ground.

The alarming spread of drugs, suicide and declining life expectancy among white working-class men is only one measure of the scope of dismay. Growing movements — Occupy Wall Street, Black Lives Matter, the young Latino Dreamers, the “Fight for $15” campaign (referring to the hourly minimum wage) — reflect the growing demand for change. The hopes roused by Obama’s historic election have largely run aground on Republican obstruction.

In this context, Sanders offers a clear and passionate vision. He indicts an economy rigged by and for the few, and a politics corrupted by big money. His calls for fundamental reforms: Medicare for all, tuition-free public college, a $15 minimum wage, fair taxes on the rich, breaking up big banks, re-making U.S. trade policies and meeting the challenge of climate change. He summons a “political revolution,” of millions of people standing up to push politicians to respond. Sanders has walked the walk — funding his campaign with literally millions of small donations, spurning the creation of Super PACs to collect large and dark contributions from the wealthy and corporations.

Clinton dismisses Sanders’s agenda as unrealistic. Former President Bill Clinton scorns it as a “cartoon.” She’s made herself the candidate of continuity by defending Obama’s reforms, drawing distinctions mostly by being more hawkish on foreign policy. Hillary Clinton argues that progress can only come one step at a time — reaching out and seeking to find “slivers” of common ground with Republicans. She touts her experience and her skill at negotiating in back rooms to make progress.

In face of the Sanders challenge, Clinton increasingly sounded like the “No We Can’t” candidate. As New York Times op-ed columnist Charles Blow, among many others, has argued, she has yet to show that she has a vision that can provide hope and inspiration and can mobilize voters. Yes, electing the first woman president would be historic — but thus far it has not been enough.

This is also a battle over what the Democratic coalition looks like, who Democrats are and whom they fight for. Clinton seeks to consolidate the current arrangement — collecting upscale professionals repelled by Republican social conservatism and linking them with unmarried women, people of color and the young. With financing from Hollywood, Wall Street and Silicon Valley, the party leads with its social liberalism linked to an established moderate economics. What Bill Clinton’s New Democrats once worried were damaging wedge issues now play in Democrats favor.

Sanders seeks to consolidate a coalition based upon his core economic and political populism, without abandoning social liberalism. He recognizes that single women, people of color and the young are united largely by their need for fundamental economic and political reforms. The authenticity of his appeal — his willingness to call out America’s rigged economy and corrupted politics — give him the possibility of reaching into the white blue-collar workers, who Trump has already shown are shunning establishment Republicans.

Hillary Clinton, of course, remains the prohibitive favorite to win the 2016 Democratic nomination. The argument about Sanders viability is, in some ways, a distraction. She has to show that she is viable electorally by laying out a vision and agenda that rouse energy among the Democratic base. If she does that, she could provide the best proof of Sanders’ lack of viability by beating him.

Correction: The final results in the Iowa caucuses have been updated in this article.