Political reality in america is that there were multiple changes of ruling party in the last decade and MPs being voted out on specific issues. Of course a representative multi-party system would be preferable, but it's not that it's impossible to achieve anything at all.
I think you don't understand the American political system. At present there are only two parties in terms of realistically getting elected. There is no such thing as a ruling party in the sense of European parliaments. Members of a party are free to vote as they please. Hence Lieberman famously derailing aspects of Obamacare. There is also the fact that both parties in the U.S. have shifted very much to the right the last 40 years. The reality in the U.S. is that even with our so called left leaning party in power in the legislative branch and executive branch no serious environmental accords were negotiated and passed.
