Well, I suppose the phrase "meaningful" is a bit loaded, but I would argue that most bills passed since the 70's have been mostly window-dressing, designed to look good without actually solving anything. And I think that the emphasis has shifted away from solving problems and towards looking like you care about solutions.
And I will place the blame on the rise of info-tainment media.
Since news came to television and turned into a massive entertainment industry (and if you think TV news isn't an entertainment industry, I would direct you to Neil Postman's books on the subject). It's been fast-food-ified. The American people have more and more access to more and more information, but that information lacks nutrition. We get sentences, not paragraphs; headlines, not stories; positions without supporting arguments.
This has resulted in a country that is measurably irrational. Jacob Weiberg did a fabulous piece for Slate depicting just this phenomenon. A large majority of the people opposes extending the Obama stimulus. But a larger majority (we're talking over 80% here) supports extending unemployment benefits--which is a stimulus program!
Which means we have a state of political paralysis. How can a legislative body legislate when it is scheduled for upheaval every two years by a fickle America populace? No wonder politics has been absolutely reduced to pandering. And I honestly don't know if this situation is truly recoverable.
The age of American dominance may be ending sooner than we think.