The character of the man or woman who would be President matters a great deal. So while isolated incidents that raise the eyebrows of voters and pundits may not initially be worth pursuing, when a pattern develops, those incidents are worthy of journalistic pursuit.
Re Mrs Clinton, the Bosnia incident played into the storyline so well illustrated by Christopher Hitchen's book, No One Left to Lie To: The Values of the Worst Family.
Re Mr Obama, his attitude toward the country he seeks to lead has become suspect because of a series of incidents. And while some may seem trivial when considered alone (how he stands during the Pledge, why he won't wear a flag lapel), when viewed in context with his very close association with a man who says "God Damn America," his much less significant association with an unrepentant bomber (imagine if it was not Mr. Ayers but Mr. Rudolph, the abortion clinic bomber), a comment where he essentially called many of the Joe Six-pack Democrats bigots (and did it with elitist-sounding language), and even a wife who has suggested less than love for her country--all of these incidents have formed a narrative that journalists should explore. Sure as shootin', the GOP groups are going to explore the narrative big time come fall.