Tyler Cowen argues in the New York Times that money doesn't necessary buy the votes of members of Congress, but influences their access to ideas and information.

The Supreme Court’s recent ruling on campaign spending also comes into clearer focus through the median voter theorem. The court ruled that the government may not ban political spending by corporations in candidate elections. Critics fear that the political influence of corporations will grow, but some academic specialists in campaign finance aren’t so sure.

For all the anecdotal evidence, it’s hard to show statistically that money has a large and systematic influence on political outcomes. That is partly because politicians cannot stray too far from public opinion. (In part, it is also because interest groups get their way on many issues by supplying an understaffed Congress with ideas and intellectual resources, not by running ads or making donations.) It is quite possible that the court’s decision won’t affect election results very much.