Americans have unspoken yet clear expectations when it comes to presidential candidates and how they dress.

Too much polish suggests a pretentiousness, perhaps even a slickness, while inadequate attention to appearance suggests disorganization, unprofessionalism, even an unfitness for office. Those campaigning for the highest office in the land must look serious yet approachable, and American voters respond favorably when they strike that balance.

Whether by intent or accident, a candidate's appearance provides clues about personality, judgment, values and priorities. And for some who would be commander-in-chief, the added baggage of gender or race can make navigating the sartorial waters even more perilous.

How the three U.S. senators vying to be the next occupant of the Oval Office are attiring themselves reveals something about the candidates and the mindset of the electorate. John McCain tends to look bland and dated, Barack Obama needs to dress more maturely, and Hillary Clinton -- who has the most potential pitfalls to dodge -- also could benefit from some minor adjustments.

It's no surprise that Mr. McCain, 71, the de facto Republican nominee, dresses the most conservatively. Combined with his white hair, his nondescript business suits and penchant for pale ties make him appear almost grandfatherly.

He seems even more dated alongside his wife, Cindy, 17 years his junior and a former rodeo queen who is always immaculately turned out.

There's nothing wrong with a grandfatherly appearance if it's modern and inviting. But Mr. McCain's attire depersonalizes him, making him somewhat forgettable and a little crusty. Even the casual shirts he's been wearing lately as he informally greets voters look like thrift-store finds.

Conservative doesn't have to mean dull and washed out. Mr. McCain is passionate, and his attire ought to better reflect his vigor and strong personality. He wore richly colored neckties in a few debates, and he needs to wear them more often.

Mr. Obama, 46, faces a different set of challenges.

His go-to look is a dark, simple suit with a white shirt and a dark thin tie. It has the feel of a uniform and conjures the image of young activists in black-and-white photos from the Civil Rights Movement. As such, it subtly reflects the countercultural tenor of his candidacy.

Mr. Obama also has a special line to tread as an African-American man. If he appears highly polished -- French cuffs, flashy suits, pocket squares -- he risks looking like a stereotypical city slicker. Too casual -- going without a tie and a jacket at the same time -- might make him indistinguishable from the average black guy on the street, a visual with its own set of social baggage.

He sometimes wears suit jackets that are boxy and ill-fitting. The look probably resonates with young male voters, who tend to wear clothes that are too big. But combined with Mr. Obama's boyish face, ill-fitting jackets make him look like a political novice.

Lately, he has begun wearing jackets that fit better, resulting in a more presidential look. Jackets with peak lapels would broaden his chest and shoulders and balance his thin frame, drawing the eye upward.

Although, he appears to have survived the flag-pin flap, it wouldn't hurt Mr. Obama -- or any other candidate, for that matter -- to always wear one. Many Americans read something into the presence or absence of such symbols.

Mrs. Clinton, 60, has more potential to err in campaign dressing. Professional dressing is more difficult for women than men because of a wider range of options, and the chances for a misstep increase in politics because the American public is more critical of a woman's appearance.

Female heads of state in other countries don't seem to face the fashion pressures of U.S. women. German Chancellor Angela Merkel may be the most conservative, in keeping with her country's traditionally conservative aesthetic. But she doesn't shy away from colorful jackets.

Other leaders, such as Argentina President Cristina Fernandez de Kirchner and India President Pratibha Patil, often wear fashionable dresses, brightly colored accessories and stylish jewelry without their competence being called into question.

Throughout her campaign, Mrs. Clinton wisely has not dressed as she did when she was first lady. Nor has she attempted the refined elegance of House Speaker Nancy Pelosi, whose chic skirt suits and scarves are too soft and ladylike for a presidential campaign.

Mrs. Clinton's skirts remain out of sight and dresses are totally out of the question as she attempts to walk the fine line between authoritative and feminine. It's as if the two cannot co-exist -- which they likely do not in the electorate's mind when all of the presidents have been men.

Thus, a skirt would be a constant visual reminder that Mrs. Clinton is a woman, and a woman has never occupied the nation's highest office. Even a skirt of conservative length would necessitate shoes with higher heels, compounding a visual inconsistent with the man-in-pants image with which Americans have become accustomed and comfortable during presidential elections.

To slightly defeminize one's appearance does not automatically masculinize it, and Mrs. Clinton has found a safe middle ground in slacks and jackets. These separates can visually elongate the body, a benefit when one considers that Americans historically favor tall presidential candidates. A jacket and slacks also can camouflage the types of body issues for which women, especially middle-age ones, are routinely critiqued.

Along with slacks in dark or neutral colors, Mrs. Clinton has been wearing boldly colored jackets and separates that don't cross the line into excess. The shades of blue, red, yellow and orange are uplifting and feminine without being exuberant and girly.

At the same time, she should incorporate softer blouses with more obtuse collars. Her large pointy collars veer toward sharp and stiff -- not an ideal association to create when you're trying to combat a perception that you have a polarizing personality.