Whether or not Democrats retain the Presidency, Republicans will continue to control at least the House, and without filibuster reform, the Senate, long after demographics turn against them.
First, there’s redistricting, which was very successful for Republicans and won’t be revisited until 2022. Sam Wang calculates that Democrats have to get 2.5% more in the Presidential popular vote to have a 50-50 chance of taking the House. Another rough way of looking at how well Republicans did in redistricting is to look at the House component of the Electoral College vote. If you look at the current electoral map, subtract the 2 electoral votes for Senators from each state, and the 3 votes for DC, Obama has 250 electoral votes. By the same math, and even giving him Florida, Romney has 185. But, if you split the difference on undecideds, the Republicans have a 40 vote advantage in the House. Using a statistical model, or a rough-and-ready electoral snapshot, we’re way behind, which means redistricting cut the Republican’s way this cycle.
As for the Senate, the 25/25 split in states (if you give Romney Florida) means that Democrats are lucky to have their roughly five seat advantage in that body, and 60/40 is a very high bar.
Second, there’s turnout. We are starting to have two very different elections every 2 years. The Presidential race is the one where energized Democrats will jump through the voter suppression hoops, and stand in line for hours, to vote for the President. Because the entire media/political complex is obsessively focused on the Presidential race, the off-year elections are to voters as the Pro Bowl is to the Super Bowl, with much lower turnout and interest. With lower turnout usually favoring Republicans, there’s certainly no obvious, easy path to the Democrats taking the House in 2014.
May be 2014 will be like 2006, and maybe Harry Reid will finally do filibuster reform, but the party that wants to legislate needs to control the legislature, and with redistricting and the natural tendency of the Senate to favor smaller, more rural states, the next few years are going to be tough for Democrats.