According to the Times of London Big Boy Petraeus is going to claim that Iran's been very, very bad as of late:
IRANIAN forces were involved in the recent battle for Basra, General David Petraeus, the US commander in Iraq, is expected to tell Congress this week.
Military and intelligence sources believe Iranians were operating at a tactical command level with the Shi’ite militias fighting Iraqi security forces; some were directing operations on the ground, they think.
Maybe this isn't the casus belli I'm thinking it is; maybe the Times is accurate in that Petraeus
intends to use the evidence of Iranian involvement to argue against any reductions in US forces.
All I know is that there are a lot of people out there who are wondering why we haven't attacked Iran already if "they're killing our troops", and this is just going to encourage them all the more.