I understand Givhan's reportage as reflecting the valid observation that one's clothes say something about the message that one is attempting to convey. If, for example, Senator Clinton were to wear pajamas to a televised debate, one could fairly comment on her apparent failure to take the event seriously. For this reason, Givhan was right to report on Vice President Dick Cheney's decision to wear a parka, a knit ski-cap, and hiking boots to the ceremony at which world leaders had gathered in Poland to commemorate the 60th anniversary of the liberation of Auschwitz. While others wore dark overcoats, reflecting the solemnity of the occasion, the representative of the United States, as Givhan colorfully described it, "was dressed in the kind of attire one typically wears to operate a snow blower."
What distinguishes such examples from the "cleavage" case is, first, that the former represent major departures from customary behavior, while the latter -- even if a V-neck is relatively unusual -- really does not. Second, the former do not draw attention to the wearer's identity as a sexual being. This second point is important, because membership in a traditionally excluded group means that distinctiveness can be viewed as suspicious (or "provocative").
For a provocative example, consider beards. Just as as breasts are a "secondary sex characteristic" in women, a beard is a secondary sex characteristic in men, resulting from an interaction between sex hormones in the bloodstream and skin. Yet no one thinks of a man who grows a well-groomed beard as "immodest" or provocative. In a female-dominated world, one might imagine outrage at a man's willingness to "expose" his facial hair for public consumption. One might demand, in fact, that he "cover it up," particularly when in the presence of women.
I mean here to raise consciousness about our hidden assumptions, not to offer an actual policy or to insult readers who have beards (either as a fashion statement or because they find shaving uncomfortable). The reason we do not view beard-wearers as immodest or exhibitionistic is that beards represent one variant on the way that ordinary men appear. And ordinary men are the "norm" in public life. A beard will rarely if ever attract sexually charged critique in major newspapers (apart from, perhaps, an observation about whether the new look flatters the wearer or not). For a woman, however, any look is a gamble. As Senator Clinton knows, the wearing of bland pants suits can attract negative remarks because it seems to represent a masquerade of sorts -- a woman who dresses like a man even though she obviously is not a man. Is she afraid or ashamed of her femininity? If, on the other hand, she wears a v-neck, we hear that she has communicated a request to be viewed in a sexual way.
Almost by definition, the first woman president -- and the first frontrunning female candidate for president -- will be experimenting with fashion, no matter what she decides to wear. When the media highlights this experimentation, particularly in an obnoxious and nasty way, however, it forces women in politics to dedicate precious resources to what is ultimately a trivial distraction from substance.