Susan Page

USA TODAY

Hillary Clinton is poised to break historic ground Tuesday, but the latest research shows that she and other women still traverse a more difficult political landscape than men when they run for office — and that those differences exacerbate some of the most serious challenges she faces about honesty and likability.

While more than 100 men have been nominated for president by the nation's dominant political parties over the past 220 years, when the polls in New Jersey close Tuesday night, Clinton is expected to become the first woman to clinch the nomination of a major party for the nation's highest office.

"It's the ultimate treehouse with a 'no-girls-allowed' sign posted on it, and it would be absolutely wonderful to have her break into the treehouse and take the sign down," former Colorado congresswoman Patricia Schroeder says of the White House. Even so, Schroeder, 75, says the gender-based hurdles and stereotypes she faced in her own bid for the Democratic nomination in 1988 now are "more subtle, but it's more of the same."

For instance, a report this spring by the Barbara Lee Family Foundation found that voters are willing to support a male candidate they don't like if they think he is qualified. But they are less likely to support a female candidate they think is qualified unless they also like her. "For women candidates, likability is linked to electability, and that's not the case for men," says Adrienne Kimmell, executive director of the nonpartisan institute.

In this year's campaign, voters view Clinton and presumptive Republican nominee Donald Trump unfavorably by record levels -- 54% for her and 61% for him in the latest USA TODAY/Suffolk University Poll -- but the study indicates that she is more likely to lose votes as a result than he is.

In a classroom study at Macalester College in St. Paul this year, an analysis of media coverage of Hillary Clinton, Democratic rival Bernie Sanders and Republican hopeful Ted Cruz came to a similar conclusion. "Although Ted Cruz was often tagged for being not very likable, it didn't seem to be as much as a detriment to him as it was for Hillary Clinton," says political science professor Julie Dolan, the lead author of the 2016 edition of Women and Politics: Paths to Power and Political Influence. "Clinton received more personal coverage than did Cruz, despite already being a much better known political figure, and her coverage was much more negative than his.”

When it comes to honesty and trustworthiness, Americans automatically give an edge to women. In a Pew Research Center Poll released in January, 31% said women were better at being honest and ethical; just 3% said men were better. But studies show that women pay a higher price than men when they aren't seen as honest, and have a harder time regaining trust if they lose it.

That's true in fields other than politics. A new academic study by Wharton professor Mary-Hunter McDonnell and others into disciplinary punishments imposed by the American Bar Association, first reported by NPR, found that female lawyers were twice as likely as male lawyers to be disbarred when accused of virtually identical infractions.

For Clinton, perceptions that she can't be trusted, stoked by ongoing investigations into her exclusive use of a private email server when she was secretary of State, are seen as one of her biggest liabilities in the campaign. Nearly two-thirds of likely voters in a CBS News/New York Times poll last month said Clinton wasn't honest or trustworthy -- though those are the same dismal ratings Trump received.

Now Trump routinely derides Clinton as "Crooked Hillary."

"When women are pushed off of or fall off their honesty-and-ethical pedestal, it is very, very hard for them to climb back up, and that isn't the case for men," Kimmell says. Male candidates face lower expectations that they will be honest, and voters are quicker to forgive them when they aren't.

"You know that former governor of South Carolina who's now a member of Congress?" she asks, a reference to Mark Sanford. While governor, he was censured by the South Carolina General Assembly for personal misbehavior, then won a special House election four years later. "If 'he' were a 'she,' that couldn't happen."

'A SEA CHANGE'

To be sure, some barriers for female candidates have been lowered. In a 2013 book titled He Runs, She Runs, Dartmouth professor Deborah Jordan Brooks argued that gender stereotypes don't hurt female candidates, especially as more women seek and win office.

"When I started out in 1972, it was practically impossible," recalls California Sen. Barbara Boxer, retiring this year after four terms in the Senate and five in the House. "I lost a local county supervisor race because people wrote that I was abandoning my children." Her memoir, The Art of Tough, was published last week by Hachette.

"There's been a sea change," Boxer said in an interview. "But are there still challenges; are there still prejudices? Absolutely."

In an interview with USA TODAY two years ago about her memoir, Hard Choices, Clinton predicted that a woman running for president in 2016 would encounter a friendlier political landscape than she did in her failed 2008 bid. "It feels different," she said. "It feels like our country, our society — we've gone through a learning process." While there would be "vestiges" of sexism, "I do believe it would not be as reflexive. It would not be as acceptable."

Clinton starts out having surmounted some of the hurdles female candidates typically encounter.

"She's not your typical woman candidate in the sense that the Number One thing most women have to do running for executive office is prove that they're qualified, prove that they're competent, and that is not something that Hillary Clinton has had to do," says Democratic pollster Celinda Lake, who has studied gender politics. "Voters from the get-go have thought that she is extremely qualified."

Clinton's four-year tenure heading the State Department also has an impact, she says. "Traditionally women have more credibility on domestic issues than foreign policy, and of course she is perceived to be extremely experienced on foreign policy."

That said, Clinton faces the same dilemma as other female candidates in trying to come across as decisive and impassioned without being accused of being shrill.

Debbie Walsh, director for the Center for American Women and Politics at Rutgers University, says commentary on Clinton's demeanor on cable news shows and Twitter proves the persistence of bias. "I mean, the conversation about ... 'why don't you smile' and 'why are you yelling at me?'" she says. "The campaign is filled on both sides with men doing a lot of yelling, and that doesn't seem to get called out in the same way."

After Trump accused Clinton of playing "the woman card," he was asked on MSNBC's Morning Joe to address her response to "deal me in" when it comes to issues such as equal pay and paid family leave. He countered by discussing not what she said but how she said it.

"I haven't quite recovered ... from her shouting that message," Trump replied.

Lake once conducted an experiment with a pair of radio ads that contained the same content but had a male voice on one version and a female voice on another. While the decibel levels were identical, listeners rated the woman's voice as being significantly louder.

"A man is assertive where a woman is aggressive," Boxer says with an edge of sarcasm. "A man has spirit where a woman is loud."

HOLDING RESERVATIONS

Some voters continue to express doubts about a woman as president.

In an NBC News/Wall Street Journal poll last month, one in five of those surveyed said they were "very uncomfortable" or had "some reservations" about Clinton as the first woman president.

(That said, Trump faces challenges as well: Six in 10 said they were "very uncomfortable" or had "some reservations" about him serving as president without having had experience in the government or serving in the military.)

In the survey, nearly one in five said they were "comfortable" with a woman as president, and more than one in five said they were "enthusiastic" about it. "It's been an asset to her campaign," says New York Sen. Kirsten Gillibrand, who succeeded Clinton in the Senate.

At a rally Friday in Culver City, Calif., Clinton reprised language she used almost precisely eight years earlier, when she conceded the Democratic nomination to Barack Obama.

"Starting next Tuesday," she said. "we're on our way to breaking the highest and hardest glass ceiling."