I do not believe that any politician, especially those at the presidential level, represent the middle or low classes. However, among the other two main candidates, Hillary Clinton and Donald Trump, I do think that Bernie Sanders seems to be the one who best represents the United States middle class.
Bernie Sanders is a rich man but he does champion the cause of the poor and disenfranchised. He has been doing that for years, not just to win an election. He is trying to get free college education for all kids, not just wealthy kids. That alone would actually change the dynamic of this society. Imagine getting a degree and not being saddled with $50,000 of student loans. That would help many people obtain the American dream of buying a house and building a career.
Bernie Sanders, like all party nominees aspires to speak to middle class concerns and values. That is the foundational approach to political strategy - appeal to the largest block of voters with themes that resonate with them. That being said, it is a reality in presidential politics that little guys almost never become players. Bernie Sanders is a big league player speaking to middle class concerns. The question really is whether he can and will deliver.
In every social system, there is the ruling class. That class gets richer and richer, supposedly for the good of everyone else, as the poor only become so poor they starve. Russia is a perfect example of this. Sanders doesn't want to be a man of the people. He wants to be a ruler of the people. He'll eat snails and shrimp while we starve.