In U.S. culture, the stereotype of Black women includes being too loud, aggressive, etc (i.e., masculine). Thus, to fit into the role of first lady, according to Reuters, Michelle Obama must “soften” herself. Note that the text accompanying this headline emphasizes that she’s just going to be a mom.
In contrast, Cindy McCain already “fits” “with her elegant clothes and pefectly coiffed blond hair.”
See also this post where Michelle Obama is called an “angry black woman.”