The Blue Wall

I've already come out as agreeing with Jon Chait that Hillary is the favorite in 2016.

Vox laid out some reasons why Hillary might not be the favorite.

Foremost is the idea that Hillary will be running for Obama's third term, and that's hard, historically.  However, if that's true, the lack of an intraparty challenge is a huge advantage for Clinton.  When incumbent presidents are challenged within their party (1912, 1968, 1980, 1992) they lose.  Obama isn't running, but Democrats will be able to unify around the idea of a third term protecting Obamacare, keeping America out of Middle Eastern wars, changing the Supreme Court and trying to prevent a full-bore plutocracy.  That matters.

Another argument that Nate Silver makes is that fundamental change rarely really occurs in American politics, which is true until it isn't.

They show this chart:

It shows the lack of landslides in the last 30 years (since 1984).  In fact, we have become much more polarized as a country, with Red States and Blue States, City and Country.  Part of the population is irrevocably Democratic and part is irrevocably Republican.

And the Democratic part is bigger, at least in terms of population.

Republicans can and will have an advantage in the House, because they can win rural districts 55-45 while Democrats win concentrated urban districts 80-20.  But while that means the GOP can send a Republican majority House delegation from Pennsylvania, it doesn't mean Scott Walker can beat Hillary in Pennsylvania.

If we make the following states toss-ups (NH, FL, OH, VA, WI - for Walker) but leave MI, MN, CO, NV and NM as Democratic states (which I think is a good bet), then Democrats START at 252 electoral votes.  That's just be being the Democratic candidate.  If the GOP nominates Bush or Rubio, Clinton wins Wisconsin in her sleep (262) and probably NH (266).  That means either Iowa, Ohio, Florida or Virginia gives her the presidency.  Frankly any state of any size: Georgia, North Carolina, Missouri, Arizona...You name it.

The presence of a Republican Wave in 2016 would be predicated more on a Democratic collapse than a Republican resurgence.  A second recession, a scandal, a military humiliation...That's what the GOP is banking on to win.