The 300 US troops being sent to Iraq as “advisers” for the Iraqi military were by and large already in Iraq and set to go, but are holding off getting involved in the ongoing war until Iraq agrees to give them legal protection.
The US withdrawal from Iraq at the end of the last occupation came primarily because Prime Minister Nouri al-Maliki was never able to get parliament to agree to give US troops immunity from prosecution under Iraqi law.
The Pentagon says they expect the same immunity this time, though it isn’t clear if the extremely divided parliament is going to be any more willing to give it this time. The more likely event would be Prime Minister Nouri al-Maliki agreeing to some sort of “emergency” provision.
It doesn’t appear as if that would actually be legal under Iraqi law, but it would likely be sufficient to give the Pentagon at least some claim to being above the law, particularly since Maliki, as the acting Interior Minister, also has total control of the nation’s police force.