Of course David Cameron has some influence on the way world politics work. He's the Prime Minister of one of the most powerful countries in the world, after all, but America is America and England is England. People in the U.S. are more concerned with what is happening in their day-to-day lives than what is happening across an ocean.
The US has its own campaign to worry about. In the past, maybe it would have affected it in a way but the 2016 campaign is different and has a unique verity of candidates with different policies. Most of them talk about reforms within the US and i don't think foreign policy would influence much
I'm quite sure that most Americans have no idea who David Cameron is. Unfortunately, Americans don't have much knowledge or interest in politics outside of The United States. I am speaking as an American. Americans care about what they see and read in mainstream news. The only thing remotely about UK politics in American mainstream news has to do with Queen Elizabeth's social events or what Kate Middleton is wearing.
Since David Cameron has been Prime Minister of the U.K. for the past five years, his re-election will not spur voting differences in the United States. In addition, Americans tend to be less aware of worldly proceedings outside of their own country, and I would go as far as to say that the average American would not be able to name the Prime Minister of the U.K. For this reason, I do not believe his victory will affect 2016's presidential election within the United States.