I strongly doubt that Bernie Sanders' presidential campaign will have a significant effect on the presidential campaign or on the mainstream media's coverage of that campaign. My doubts are based on this basic truths about the American punditocracy:
While the may media lavish attention on any fringe rightwing presidential candidate, even if he or she has no chance of ever being elected President (e.g. Herman Cain), the media will dismiss any democratic candidate who is perceived to be to the left of the party's mainstream as "unelectable" and the mainstream media almost completely ignores unelectable candidates on the left.
The parties are not covered the same way in the media and the dynamic that drives "mainstream" Republicans to the right during the primary season just don't happen in the Democratic party.
While the may media lavish attention on any fringe rightwing presidential candidate, even if he or she has no chance of ever being elected President (e.g. Herman Cain), the media will dismiss any democratic candidate who is perceived to be to the left of the party's mainstream as "unelectable" and the mainstream media almost completely ignores unelectable candidates on the left.
The parties are not covered the same way in the media and the dynamic that drives "mainstream" Republicans to the right during the primary season just don't happen in the Democratic party.