Nominating anyone other than Clinton is handing the GOP the Presidency for at least 4 years.
Is the Democratic field so bad they can't beat a really corrupt guy, the brother of a President who ended his term with a 19% approval rating, Rand Paul, or a guy who literally did a fake filibuster to fund-raise?
I'm exaggerating, but it goes from a guaranteed win to a 55/45 chance at best. A candidate like Schweitzer is a risk that could pay off or fail miserably. We don't know how well he would play nationally. Cuomo can't win in a 50/50 year and Sanders would never win. Hillary is clearly the best candidate, everyone in America has already formed an opinion on her, and she starts out in a great position in key states like FL & OH.
2008 was a heavily Democratic year and it was fine to take a risk, I can't same the same for 2016.