This is a simplistic view of American politics. "Powerful interests" do not refer to a small number of wealthy people and corporations that want candidates at odds with the public interest. Powerful interests include mass membership organizations like AARP, NRA, unions, environmental groups, education groups, etc.
Whether they are at odds with the public interest depends on what you believe the public interest is--and there are large powerful interests on both sides. Based on your previous posts my guess is that your view of public interest means liberal policies. Using that assumption, many corporations have pushed against state legislation that would allow discrimination against gays and they have been successful by threatening boycotts against those states. Many corporations fought U. S. withdrawal from the Paris climate agreement. There are many other examples where corporations or other interests pushed liberal policies. Compare the campaign contributions of business, industry, and financial firms--they overwhelmingly backed Hillary against Trump in 2016.
The point is that we are all special interests and millions of citizens who give $20 to an organization or candidate is as powerful as any other groups because they have both money and votes. Legislators react more to vote power than money because the point of money is to sway votes. Most Americans vote party and money does little to affect their votes unless you believe money persuaded you to vote for your chosen candidates. And nobody I ever talk to admits their vote was swayed by money.
Those powerful interests did not prevent any of the current liberal policies you favor and probably pushed for most of them.
