Start with this: Despite 8 years of population growth, almost exactly the same number of votes were cast in 2012 as in 2004 (121 million). That's a December count for 2012, so it's a near-final total.
In 2012, Obama ended up with 3 1/2 million more votes than Kerry got in 2004. Meanwhile, Romney ended up with the essentially the same vote total as McCain in 2008 -- which was 4 million short of Bush's vote in 2004.
I'd say that's 4 million votes that the Republicans could've had with a.) a more conservative candidate and b.) at least asking for their vote.
In fact, that brings up a largely unrecognized problem with the Republican party establishment. While they aren't bashful about outright pandering for some votes, they appear embarrassed to even ask for the votes of the so-called religious right. Meanwhile, McCain, e.g., went out of his way to insult constitutional conservatives.
No wonder 4 million stayed home.
I stand on my original contention: Republicans win when they talk, act and govern conservatively. They lose when they don't defend the conservative high ground.
The problem is simply stated: The base is ideological and anti-government. The party is non-ideological and pro-government. Meanwhile, on the left, the Democrat party and its base are both ideological and pro-government.
You know its been 8 years and a lot of those people passed away, right?
Also, your numbers are wrong. Bush got 62 million votes in 2004, Romney got 60.8 million votes in 2012. The difference was only 1.2 million votes, not 4 million. Also, Obama got 4 million more votes in 08' than he did in 12', so by your logic he left more votes on the table than did Romney. Does that mean if he ran more to the left he would have kept all his current votes and won the ones that didn't turn out. I doubt it. Additionally, while I don't have the figures at hand, I suspect the population growth is largely in demographics that are overwhelmingly Democrat (Hispanic).
While they aren't bashful about outright pandering for some votes, they appear embarrassed to even ask for the votes of the so-called religious right
Religious right candidates can win gerrymandered House districts. Those candidates tend to do poorly at the state and national level. A model that does work is Bob McDonnell of VA who is a social conservative but did not run on those issues. The country is more libertine and secular now. Social conservative, religious right candidates are going to have a harder and harder time winning statewide races and national races. Eventually the grass roots will understand that and nominate fewer of them. I know you don't want to hear that, but this is the direction the country is going.
The future Republican party is probably going to be libertarian-ish. Arguments for cuts in things like Planned Parenthood will be made on budgetary grounds, not moral ones. I'd expect bolder stands by the party and its better candidates on economic issues. The younger generations increasingly avoid the Republican brand like the plague because of the social positions. Expect the GOP to increasingly de-emphasize those issues and move in sort of a Rand Paul direction. (Rand Paul NOT Ron Paul).