I think anyone hating the US is more or less interested in murdering Bush right now, regardless of his political position.
Besides, there have been something like 6 attempts on Obama so far that I know of, the others are speculation and I won't go there. The secret service protects the political parties and their representatives, and trust me when I say it's allot easier for another state to do some damage elsewhere instead of trying to get past the secret services to assassinate someone.