Politicians are not necessarily clueless and only a minority are especially dim. When one of them is ambitious and sufficiently ruthless to achieve some of their ambitions, they start to think they really are clever instead of just moderately competent, and that their ideas must be right. Combine that with a strong belief in their own rhetorical brilliance and they think they can give speeches like this one, and convince everyone of the truth of their position.
Well, it's either that or they know they're talking bollocks but they'll get sacked for embarrassing their boss (and by extension their country) if they don't go out and try. The classic example of this was Colin Powell's speech to the UN outlining the evidence for Iraq's weapons of mass destruction and links to al-Qaeda, when he knew that Bush had already decided to go to war. You could almost see the shame dripping off him.