But these results, though worrisome for Clinton, do not address the question of how Sanders would fare in the aftermath of fierce Republican attacks. Sanders skeptics assume his support would crumble, but they also make a second, more hidden but equally crucial, assumption: that Hillary Clinton has been attacked for so long and so ferociously that she is immune to further impact. As William Saletan put it: “After three presidential elections, eight years in the White House, eight years in the Senate, and four as Secretary of State, she is one of the most thoroughly investigated people in American history ... [Republicans have] subpoenaed everything they can find on her, unloaded all their oppo, and she still wins.”

Saletan and other Sanders skeptics are surely correct in believing that Sanders’s poll ratings would drop in response to a sustained assault by the Republican attack machine. But it is crucial to understand that the charges leveled against him, some of them true and others fabricated, will all be viewed — as is the case with Hillary Clinton — through the lens of public perception of his character. Here Sanders is on firm ground: 68 percent of voters consider him “honest and trustworthy” and 70 percent say he has the “integrity to be president.” In a year in which voters crave authenticity, Sanders’s unwavering consistency, his record of taking principled but sometimes unpopular stands, and his exceptional financial probity are powerful assets.

Nonetheless, Sanders’s high ratings in character would not render him immune to ferocious Republican attacks. These attacks would almost certainly depress his poll numbers, but there are reasons to doubt the familiar narrative that Sanders would be decimated. Let us begin with the charge that he is a “socialist”; it is, after all, true, and Sanders has not hidden that he considers himself a democratic socialist. Three or four decades ago, this attack would surely have been fatal; the Cold War was still very much alive, and the Soviet Union was the international symbol of socialism. But the Cold War ended more than a quarter of a century ago, and now the word “socialism” often conjures up images of Denmark and Sweden — hardly the stuff of nightmares. Broad swaths of the American electorate no doubt find the idea of a “socialist” president unacceptable, but it is doubtful whether many potential members of a Democratic coalition would vote for Trump in response to this line of attack.

Sanders skeptics often point to the disastrous Dukakis campaign of 1988 and the notorious Willy Horton ads that helped sink it as an example of what the Republican attack machine can do to a liberal Democrat. But as Princeton historian Matt Karp has pointed out, this is a profoundly flawed analogy, for Dukakis was a stiff technocrat who, he wryly notes, “won the Democratic primary not by packing arenas with passionate supporters, but chiefly by having more impulse control than Gary Hart and being whiter than Jesse Jackson.” In May 1988, only 52 percent of voters knew Dukakis well enough to have an opinion of him, making his early lead illusory; in contrast, by New Year’s Day 2016, 85 percent of Americans had formed an opinion of Sanders.

Today’s political, demographic, and media context make it a vastly different world from 1988. Perhaps the most important difference is the rise of what political scientists call “negative partisanship“ — a sharp increase in partisanship and straight-ticket voting driven by hostility to the opposing party and reinforced by shared racial, cultural, and ideological identities. This growing polarization likely sets an upper limit on the efficacy of the Republican attack machine.

A revealing indicator of the declining effectiveness of the kind of attacks that worked so well in the past was the fate of Obama in the election of 2008. In February of that year, Clinton pollster and campaign strategist Mark Penn dismissed Obama’s strong performance in early presidential polls, arguing that “Sen. Obama has never faced a credible Republican opponent or the Republican attack machine, so voters are taking a chance that his current poll numbers will hold up after the Republicans get going.” Obama, after all, was an African-American with the middle name Hussein, and he had spent a good part of his childhood in a Muslim country. During the midst of the primary campaign, in what now seems a distant memory, a video suddenly appeared showing Jeremiah Wright, the pastor of Obama’s church, shouting “God damn America!” The attacks that followed no doubt damaged Obama with Republicans, but failed to undermine his appeal to a majority of voters. Reviewing this history, Matt Karp asks a pointed question to those who believe Sanders could not survive Republican attacks: “Why does anybody believe that red-baiting will succeed where racist innuendo failed?”

The rise of negative partisanship also gives Clinton a degree of insulation from Republican attacks, as does the public’s long familiarity with many of the likely lines of attack. But it would be a serious mistake to assume that Clinton’s favorability ratings could not drop even lower; according to a recent CBS/New York Times poll, since the campaign began in May 2015, her favorable/unfavorable rating has dropped from 35-36 to 31-52, and her rating for being “honest and trustworthy” plunged from 48-45 to 32-64. To say the least, this is not reassuring.