There is no guarantee when dealing with the US. I mean the last president pull out of an international agreement (Iran) just because he didn't like it. How can you agree to something that in 4 years might just change. Making a deal with the US is dangerous, just ask Saddam or Gaddafi.
I agree with that, but I also think that of the US issued a formal guarantee they'd only imprison him for 4 years, then a British judge would likely choose to believe it whether or not we think it should be trusted.
