Kevin Drum writes about the ongoing trend toward locked-down presidential campaigns that afford little access to the press. This is something that can be explained in pretty simple economic terms. Once upon a time media distribution channels were scarce—a handful of television networks, one or two newspapers per city—so whoever controlled those channels had a lot of power. But thanks to the rise of cable and especially the rise of the Internet, even the most prominent media figures don't control anything that's genuinely scarce. Whatever remarks or ideas Romney or Obama want to convey to the public, they can convey without catering to individual reporters' or outlets' desire for access to this or that.
In the primaries things are more plentiful and there are only finite resources available for campaign coverage. So if you want to get noticed—especially if you're a second-tier candidate—you need to do things that make reporters want to cover you.
I'm not sure this is such a bad thing. Presidential campaigns are, if anything, overcovered. The new landscape creates incentives for reporters who are good at their jobs to try to cover some down-ballot races, where there's more candidate interest in offering access. Go read Dave Weigel on Joe Kennedy III and you'll see that there's lots of good coverage to be done. Meanwhile, despite the lack of journalistic access I think we have a pretty good idea of what agenda the candidates are running on. There are big unanswered questions about what a Romney administration or second Obama term would look like, but those are mostly questions about how Congress would react to the Romney or Obama agenda rather than questions about what that agenda would consist of.