If you understand the graph here to the right, you basically grasp everything you really need to know about the Big Big Picture in American Politics.
No hyperbole intended.
We can talk all day about specific policies -- Medicare, Social Security, defense spending, foreign policy, gay marriage, balanced budgets, capital gains taxation, hurricane readiness, or whatever other issue is on the current radar. All those things are very important in and of themselves.
But let's get back to the graph: A national "Winner Take All" Presidential system like the one we have in the U.S. is always going to do one particular thing: it's going to push the national parties towards the middle.
Why? Because they're out to capture votes, that's why.
A winner-take-all system doesn't lend itself to extremist parties finding their way into power, because it means that another party could capture the entire "rest" of the spectrum (remember, the first horse past the post takes the whole enchilada here). If any party parked itself right along the Liberal or Conservative "hash marks" above, it would only capture voters at that point and further out towards the fringes.
That's why some of the gloating editorials you're seeing today are so completely off-the-mark. I read a particularly bad one in the NY Times at oh-dark-thirty this morning that implied the Republican Party O'White Male Dinosaurs is ready to just be taken out behind the barn and put out of its misery (never mind its 30+ governorships, several of which are held by people who aren't middle-aged white males).
Some of the going "wisdom" suggests that demographics are going to morph the nation's political landscape into a long-term era of one-party rule. [N.B. Any time you hear anyone heralding a coming period of 'long-term one-party rule,' you should be reasonably worried. In case you need to know why, go stand at the corner of Branch and Coral, and ask anyone over the age of 30 how they feel about a single-party that knows what's best holding all the reins and not letting go].
What this so-called "wisdom" ignores is that the pendulum will swing along with the demographic landscape. Inevitably, in order to capture votes, the national GOP will adopt policies that are popular across a wide range of the spectrum (look at what Clinton did so well in 1992 to break a 12-year GOP reign in the White House). This will in turn attract new voters, and new leaders, which will eventually weaken the grip of identity politics on party affiliation in the U.S.
In some particular states, there are factors that lead certain parties to dominate (i.e. Dems in MA legislature, Repubs in Wyoming, etc.) However, the median voter theory basically means that many still govern from the center...(notice the prevalence of DINOs on Beacon Hill).
Nationally, the party that can capture that proverbial Median Voter is going to win the day. Sometimes that means parties will co-opt the other party's most popular ideas (look at Clinton, look at welfare reform, and look at how he sailed to victory in 1996). When that happens, the co-opted idea essentially comes "off the table" because it stops being a wedge between the two sides.
The Republican Party of 2042 isn't going to look or sound exactly like the Republican Party of 2012. Ditto for the Democrats. New allegiances will be made, new coalitions will be formed, and new leaders will be elected. Voters who are currently ignored by both major parties will find themselves being courted by both major parties as the landscape shifts.
So if you run into anyone today who is stocking up on champagne bottles, plastic top hats, and noisemakers in order to herald some coming era of a benevolent, utopian, one-party rulership, I would ask you to ask them to hold the phone on that celebration. Should they come back at you with almanacs, statistical registers, and other forms of demographic "proof" that this is truly happening, I would start by presenting the median voter graph above, and then ask who anointed them to speak on behalf of such huge swathes of people who are apparently incapable of choosing between alternatives.