ALTOONA, Iowa — Presidential elections traditionally speak to future aspirations, offering a vision of a better tomorrow, the hope and change of Barack Obama or the compassionate conservatism of George W. Bush. Yet this year, even before a single vote has been cast, a far darker sentiment has taken hold. Across Iowa, as the first nominating contest approaches Monday, voters plow through snowy streets to hear from candidates, mingle at campaign events and casually talk of the prospect of World Wa