Iran is determined to become a player in international politics, and I believe will stop at nothing to remove a US presence from the middle east forcefully.
The Revolutionary guard is already patrolling the same area of the gulf as our carriers and its not hard to believe the revolutionary guard will attempt some antics that will draw us into firing upon them, giving Iran cause to retailiate against the United States, causing war between Us and Iran.
http://www.worldnetdaily.com/news/article.asp?ARTICLE_ID=53577