I don't think it's fair to say that all realignments happen for the same reasons. 2008's success & future success at that is marked by that of the Millennial generation and the fast growing non-white population, who votes pretty solidly Democratic. The voting patterns of non-Millennial whites hasn't changed a whole lot, and if anything it might actually be slightly more Republican in 2016 than the average of the past 6 presidential elections. Also, because turnout is usually a lot higher in presidential elections, when younger voters come out to vote, they have greater influence and thus it would be easier to see changing preferences play out first in presidential elections. The voting patterns of young adults is critical to understanding the future composition of Congress and state legislatures, while older voters may be split at the presidential level and state level as state/Congressional politicians only have to run on views palatable in their state/district to win over those voters, as opposed to a presidential candidate who has to run on views that appeal to the broadest national audience, which will inevitably alienate certain regions. Think Rubio vs Larry Hogan (R-MD).
Also, the Solid South gave the Democratic party a nice cushion in Congress as they could lose seats everywhere else and still be able to rely on those sweet, sweet Southern seats to keep their majorities in Congress relatively healthy. Obviously those allegiances have changed, and because it's no longer solidly Democratic, it is a bit weaker as the large population of African Americans in the South still votes almost unanimously Democratic.
There are also other reasons why Democrats have a disadvantage in Congress right now. Their voters are simply not distributed as evenly. Republicans have a representation bias in both the Senate and House. Sparsely populated rural states get just as many senators as a large state like California, and these states are sometimes very conservative. Further, the clumping of Democratic voters in population centers creates packed districts where there are regular landslide elections and thus wasted votes. This also makes gerrymandering a lot more effective.
This is worth a read as well:
http://www.people-press.org/2011/11/03/section-1-how-generations-have-changed/
Because of the increasing rarity of split ticket voting, you can probably expect a continuing lag between presidential dominance and Congressional dominance, absent a major event like the GD. Younger voters fueling presidential victories won't vote more reliably in midterm elections for many years.
Um like Rhode Island, Delaware, and Vermont for the Dems? Texas is the 2nd most populous state and they get 2 US Senators just like CA does. Most of the smaller Republican States are out west like Utah, Idaho, Kansas, Nebraska, and South Dakota.
