It's not that independent parties are silenced, it's that they don't have the money to afford things like television spots. And (PLEASE! correct me if I'm wrong) I believe they need to collect a certain percentage of the votes to be eligible for the national debate which is why Ross Perot was included back when he was running.

As previously noted, this IS a republic. We directly elect people to vote for us.

Lastly, though it would be 2 decades of Bush and Clinton, it would be the American public who made it that way. Not to mention, 2 decades is deceiving-- 12 years of Clinton and 12 years of Bush is more accurate.