We have institutionalized bribery in the form of lobbyists. Liberal politicians and media outlets are just as beholden to corporate interests. All American politicians are elected by donors, not voters. The Obama response to the financial crisis was identical in every way to the response begun under the Bush administration. Democratic opposition to health reform was even cheaper and more effective for insurance companies to buy than Republican opposition.
Conservatism is a means of marketing our oligarchic system to the masses by using fear, xenophobia and religion. Liberalism is a means of marketing the exact same oligarchic system to the masses using the promise of peace, equality and multiculturalism.
I think there are a few things we could try:
1. Publicly funded elections. Sure they aren't perfect but at least it's a step to getting the oligarchical influence out of the election process.
2. Disqualification of voting rights if a congress person has taken money from a group that directly benefits from legislation. If Sen. McCain took 200k from Genentech- he gets no vote on any legislation that would directly effect them- healthcare bill, stem cell research, etc.