Hillary Clinton's favorability ratings are historically dreadful — and getting worse. Check this out:

Those numbers are abysmal. And they mean that Hillary Clinton is more unpopular than any presidential candidate in either party since 1984 (except for Donald Trump, of course).

So, faced with a skeptical electorate that dislikes her personally, what should Clinton do to improve her numbers? Well, she might try what other candidates have done in the past — and get her spouse to speak for her.

On first blush, it's an appealing strategy. After all, Bill Clinton remains very popular. And indeed, candidates' wives have traditionally been powerful surrogates who have been deployed to testify to a spouse's humanity, goodness, and general likability. In 2012, Mitt Romney was perceived as both venal and robotic, with 47 percent of the electorate viewing him unfavorably. Ann Romney, though, was viewed unfavorably by only 30 percent of the electorate. Predictably, the Romney campaign was eager to use her to bolster her husband, and gave her a high-profile speech at the Republican convention in which she talked about Romney as husband, father, and good egg.

Michelle Obama, for her part, was perceived positively by fully two-thirds of the 2012 electorate. During the campaign, Obama adviser David Axelrod described her as, "next to the president himself, and maybe including the president... our most in-demand surrogate."

Why are candidates' wives so much more popular than the candidates themselves? It's in large part because candidates' wives appear to be above the partisan fray. "First ladies can appear non-political," Denise M. Bostdorff, a communications professor at the College of Wooster, told The Week. "They're the nice person who's not really involved in politics, and people are expected to not really attack them for political positions." As a result, she said, they "are allowed to be a salesperson for the president. They can talk about all the wonderful things that he has done," without seeming like shills. Bostdorff pointed to Elizabeth Dole, who at the 1996 convention "walked out Oprah style among the audience members" to discuss, as Dole put it, "the man I love."

Elizabeth Dole was herself a seasoned politician; in 1996 she had already served in multiple Cabinet posts and she'd go on to become the first female senator from North Carolina. But she embraced a traditional role in the campaign, presenting herself as a non-political wife rather than as a partisan.

This is not something Bill Clinton has ever done, or is ever likely to be able to do. And this is why he's such a lousy political spouse.

Bill Clinton's approval ratings are in the high 50s, and he's been a vocal and active campaign surrogate. But he's never going to be anything other than a political figure, tightly bound in the public memory to his own presidency — as his tense exchange last month with a Black Lives Matter activist underlined. Bill can say that Hillary's policies are good; he can say she is dedicated and has the interests of the public at heart. But he can't say, as Ann Romney or Elizabeth Dole or Michelle Obama did, that "as a non-political figure, purely from a personal standpoint, I can tell you that my spouse is a good person." Bill can help Hillary in many ways. But his own political history prevents him from humanizing her in a non-political way.

But it's more than Bill's political history — it's his gender, too.

Politicians are supposed to be both tough and human, both unbendingly resolute and nice. For women, the demand to be simultaneously strong and compassionate can be especially difficult — not least because the way in which candidates generally broadcast their compassion is by having their (stereotypically female) spouses vouch for their hidden, lovable side.

In fact, many of the more bitter criticisms of Hillary are precisely that she has no personal self, that she is nothing but "political ambition in a pantsuit," as the conservative writer Jonah Goldberg charmingly put it. Men who want to be president point to their wives to show that there is more to them than political calculation. Clinton can't do that, both because of who her husband is, and because he's a man, and so can't immediately symbolize private life, love, and all the softer emotions which women are supposed to embody.

Hillary Clinton has been in public life for a long time, and there's a litany of good reasons to dislike her. Still, it seems likely that some part of Hillary's high negatives are due to the fact that her spouse, for all his skill on the trail, is the wrong gender to assure people that deep down, she's a good person.