Corruption is indeed one of the biggest problems in modern democracies, specially in the US. But corruption aside, the two party system is still a huge burden for the US democracy. The variety of opinions in society is huge and two parties could never represent that. You’re either for something, or against. In every political matter! In a multiple party system however, a party can side with party A on an economical matters and side with party B on infrastructural matter. A process like that eventually leads to better democratic compromises.