I've got a law degree (speaking in the hypothetical sense here), was pretty sparse on the science courses (I went with my cognitive strengths, as do most people), and eventually pursued my lifelong dream of becoming the US president. (I'm a narcissist. Sue me.) There are thousands of issues people are asking me about, and for some insane reason, people and the press expect me to have an answer to each one.
Most importantly, I can't look too bad when one of my competitors has an answer that sounds reasonable. So I talk to my advisers, get briefed on all the matters of state, both pressing and esoteric. Along the way, I hear a little about Yucca Mountain, and it sounds like a bad idea. So when asked, I say so. I throw in a little about transport by rail, because that, I understand. What the hell do I know about half-lives, groundwater plumes, seismic activity and the durability of concrete?
Have I researched the idea in depth? Of course not. Am I a nukular physicist? God help us, no. After receiving some sound, expert advice, might I change my mind? I hope so (though excoriation in the press, yet again, doesn't much appeal).
You're just looking for an excuse here. You outta' look harder. Otherwise, you might find yourself supporting someone who had Jesus appear to them in a dream, telling him that Yucca Mountain was definitely the way to go (not that any candidate would be inclined to disclose this, or anything). By your logic, certainty could easily masquerade as thoughtfulness.
Your post is just a little microcosmic example of the idiocy of pretending that our commander in chief is going to have a well formulated policy on every damn topic. Nuclear waste storage is an important issue, and needs to be considered in multiple contexts (security, energy policy, environment etc.). Were I running for office, really, I wouldn't go too far down that road until I actually attained office. I'd be too busy trying to get elected.
Wouldn't you?