A recent study (pdf) found that elite opinion, but not popular opinion, influences policy. Larry Bartels unpacks the research:
In their primary statistical analysis, the collective preferences of ordinary citizens had only a negligible estimated effect on policy outcomes, while the collective preferences of “economic elites” (roughly proxied by citizens at the 90th percentile of the income distribution) were 15 times as important. “Mass-based interest groups” mattered, too, but only about half as much as business interest groups — and the preferences of those public interest groups were only weakly correlated (.12) with the preferences of the public as measured in opinion surveys.
Drum adds his analysis:
When the preferences of interest groups and the affluent are held constant, it just doesn’t matter what average folks think about a policy proposal. When average citizens are opposed, there’s a 30 percent chance of passage. When average citizens are wildly in favor, there’s still only a 30 percent chance of passage. Conversely, the odds of passage go from zero when most of the affluent are opposed to more than 50 percent when most of the affluent are in favor.
The Dish 