here is why -
1. Obama has not converted one McCain voter. thus - Romney starts w basement of about 47.
2. many repubs stayed home in 2008 when Obama was looked destined to win.
3. 2008 - RECORD demo turnout. 2012 will see less demo turnout and more repubs.
4. Romney is better funded than McCain was and is not being outspent 3-1.
5. the GOP base is more behind Romney than they were McCain. Whether it’s the lack of palin or the hatred of Obama - GOP base is more fired up.
6. No “old man” or “ dumb bimbo” factor like in 2008.
7. Obama got a lot of crossover votes in 2008 that are now going to Romney.
8. indes favor Romney by a good margin
9. Obama now has a record. Blaming bush is old.
10. Obama’s so called “history making moment” is long over. people don’t. Give a shit anymore.
11. Romney / Ryan is way better than McCain Palin presentation wise.
12. Obama won’t get the youth turnout he did in 2008 and old people are PISSED off.
13. Blacks and Hispanics will not be fired up to race to vote for Obama like 2008.
14. Four years of Obama cured white guilt.
I think your analysis is excellent, and arguably more important than the polls. Starting with your baseline point #1, that the 2008 election provides a floor for Romney. Does anyone have any evidence that 2008 McCain voters would now switch to Obama??? That number is very close to zero.
I can elaborate on a couple of your other points, although it is somewhat anecdotal.
First, McCain scared a lot of women. Some women I know that voted for Obama (and are now embarassed by it), state that their reason was that McCain seemed to want to go to war too much. He scared them. I did not see it, but it is an interesting observation that women did. Romney does not scare women, he reassures them. Indeed, his campaign seems to know this and his performance during the last debate seemed to reassure many. So, the women vote is moving towards Romney strongly compared to McCain 2008.
Second, your point 12: Obama has lost much of the youth vote. I have two kids in college and they tell me that the Obama magic is largely gone. Interestingly, the person that attracted the most youth vote enthusiasm on campus was Ron Paul. As much as many do not like Ron Paul, it seems we will have to give him credit for attracting a lot of youth to the Republican / Libertarian party. Many of those libertarian youth voters will move to Romney now (some will vote for Gary Johnson). But, none are going to vote for Obama.